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\deflang2057\pard\plain\f2\fs20 This FAQ archived and provided free as a courtesy by
\par
\par The Providence Cooperative
\par
\par http://www.providenceco-op.com
\par
\par =======================================================================
\par
\par Version 2.2
\par Updated 7/19/98
\par Supersedes: Version 2.0
\par
\par
\par Water Treatment FAQ
\par Version 2.2
\par
\par By
\par Patton Turner
\par
\par
\par Acknowledgements: Thanks to the following people for making additions,
\par corrections, or suggestions: Richard DeCastro, decastro@netcom.com;
\par Henry Schaffer, hes@unity.ncsu.edu; Alan T. Hagan,
\par athagan@sprintmail.com; Logan Van Leigh, loganv@earthlink.net; Carl
\par Stiles, blitz1@airmail.net .
\par
\par Alan also provided the wording for the disclaimer and copyright notice.
\par
\par Copyright 1997, 1998. All rights reserved.
\par
\par Excluding contributions attributed to specific individuals all material
\par in this work is copyrighted to Patton Turner and all rights are
\par reserved. This work may be copied and distributed freely as long as the
\par entire text, my and the contributor's names and this copyright notice
\par remains intact, unless my prior permission has been obtained. This FAQ
\par may not be distributed for financial gain, included in commercial
\par collections or compilations, or included as a part of the content of any
\par web site without prior, express permission from the author.
\par
\par =======================================================================
\par DISCLAIMER: Safe and effective water treatment requires attention to
\par detail and proper equipment and ingredients. The author makes no
\par warranties and assumes no responsibility for errors or omissions in the
\par text, or damages resulting from the use or misuse of information
\par contained herein
\par
\par Placement of or access to this work on this or any other site does not
\par mean the author espouses or adopts any political, philosophical or
\par meta-physical concepts that may also be expressed wherever this work
\par appears.
\par =======================================================================
\par
\par
\par Water Storage
\par
\par -Quantity-
\par
\par A water ration of as little as a pint per day has allowed life raft
\par survivors to live for weeks, but a more realistic figure is 1 gallon per
\par person per day for survival. 4 gallons per person/day will allow
\par personal hygiene, washing of dishes, counter tops, etc. 5 to 12 gallons
\par per day would be needed for a conventional toilet, or 1/2 to two gallons
\par for a pour flush latrine. For short-term emergencies, it will probably
\par be more practical to store paper plates and utensils, and minimize food
\par preparation, than to attempt to store more water.
\par
\par In addition to stored water, there is quite a bit of water trapped in
\par the piping of the average home. If the municipal water system was not
\par contaminated before you shut the water off to your house, this water is
\par still fit for consumption without treatment. To collect this water,
\par open the lowest faucet in the system, and allow air into the system from
\par a second faucet. Depending on the diameter of the piping, you may want
\par to open every other faucet, to make sure all of the water is drained.
\par This procedure will usually only drain the cold water side, the
\par hot-water side will have to be drained from the water heater. Again,
\par open all of the faucets to let air into the system, and be prepared to
\par collect any water that comes out when the first faucet is opened.
\par Toilet tanks (not the bowls) represent another source of water if a
\par toilet bowl cleaner is not used in the tank.
\par
\par Some people have plumbed old water heaters or other tanks in line with
\par their cold water supply to add an always rotated source of water. Two
\par cautions are in order: 1) make sure the tanks can handle the pressure
\par (50 psi min.), and 2) if the tanks are in series with the house
\par plumbing, this method is susceptible to contamination of the municipal
\par water system. The system can be fed off the water lines with a shutoff
\par valve (and a second drain line), preventing the water from being
\par contaminated as long as the valve was closed at the time of
\par contamination.
\par
\par Water can only be realistically stored for short-term emergencies, after
\par that some emergency supply of water needs to be developed.
\par
\par
\par Water Collection
\par
\par -Wells-
\par
\par Water can only be moved by suction for an equivalent head of about 20'.
\par After this cavitation occurs, that is the water boils off in tiny
\par bubbles in the vacuum created by the pump rather than being lifted by
\par the pump. At best no water is pumped, at worst the pump is destroyed.
\par Well pumps in wells deeper than this work on one of the following
\par principles:
\par
\par 1) The pump can be submerged in the well, this is usually the case for
\par deep well pumps. Submersible pumps are available for depths up 1000
\par feet.
\par
\par 2) The pump can be located at the surface of the well, and two pipes go
\par down the well: one carrying water down, and one returning it. A jet
\par fixture called an ejector on the bottom of the two hoses causes well
\par water to be lifted up the well with the returning pumped water. These
\par pumps must have an efficient foot valve as there is no way for them to
\par self-prime. These are commonly used in shallow wells, but can go as
\par deep as 350 feet. Some pumps use the annular space between one pipe and
\par the well casing as the second pipe this requires a packer (seal) at the
\par ejector and at the top of the casing.
\par
\par 3) The pump cylinder can be located in the well, and the power source
\par located above the well. This is the method used by windmills and most
\par hand pumps. A few hand pumps pump the water from very shallow wells
\par using an aboveground pump and suction line. A variety of primitive, but
\par ingenious, pump designs also exist. One uses a chain with buckets to
\par lift the water up. Another design uses a continuous loop rope dropping
\par in the well and returning up a small diameter pipe. Sealing washers are
\par located along the rope, such that water is pulled up the pipe with the
\par rope. An ancient Chinese design used knots, but modern designs designed
\par for village level maintenance in Africa use rubber washers made from
\par tires, and will work to a much greater depth.
\par
\par Obviously a bucket can be lowered down the well if the well is big
\par enough, but this won't work with a modern drilled well. A better idea
\par for a drilled well is to use a 2' length or so of galvanized pipe with
\par end caps of a diameter that will fit in the well casing. The upper cap
\par is drilled for a screw eye, and a small hole for ventilation. The lower
\par end is drilled with a hole about half the diameter of the pipe, and on
\par the inside a piece of rigid plastic or rubber is used as a flapper
\par valve. This will allow water to enter the pipe, but not exit it. The
\par whole assembly is lowered in the well casing, the weight of the pipe
\par will cause it to fill with water, and it can then be lifted to the
\par surface. The top pipe cap is there mostly to prevent the pipe from
\par catching as it is lifted.
\par
\par -Springs-
\par
\par Springs or artesian wells are ideal sources of water. Like a
\par conventional well, the water should be tested for pathogens, VOCs
\par (Volatile Organic Compounds such as fuel oil or benzene), pesticides and
\par any other contaminants found in your area. If the source is a spring it
\par is very important to seal it in a spring box to prevent the water from
\par becoming contaminated as it reaches the surface. It is also important
\par to divert surface runoff around the spring box. As with a well, you
\par will want to periodically treat the spring box with chlorine,
\par particularly if the spring is slow moving. The spring may also be used
\par for keeping food cool if a spring-house is built. If this is the case,
\par it is still recommended to build a spring box inside the house to obtain
\par potable water.
\par
\par -Surface water-
\par
\par Most US residents served by municipal water systems supplied with
\par surface water, and many residents of underdeveloped countries rely on
\par surface water. While surface water will almost always need to be
\par treated, a lot of the risk can be reduced by properly collecting the
\par water. Ideal sources of water are fast flowing creeks and rivers which
\par don't have large sources of pollution in their watershed. With the
\par small amounts of water needed by a family or small group, the most
\par practical way to collect the water is though an infiltration gallery or
\par well. Either method reduces the turbidity of the collected water making
\par it easy for later treatment.
\par
\par
\par Water Purification
\par
\par -Contaminants-
\par
\par Heavy Metals
\par
\par Heavy metals are only a problem is certain areas of the country. The
\par best way to identify their presence is by a lab test of the water or by
\par speaking with your county health department. Unless you are down stream
\par of mining trailings or a factory, the problem will probably affect the
\par whole county or region. Heavy metals are unlikely to be present in
\par sufficient levels to cause problems with short-term use.
\par
\par Turbidity
\par
\par Turbidity refers to suspended solids, i.e. muddy water, is very turbid.
\par Turbidity is undesirable for 3 reasons: 1) aesthetic considerations 2)
\par solids may contain heavy metals, pathogens or other contaminants, 3)
\par turbidity decreases the effectiveness of water treatment techniques by
\par shielding pathogens from chemical or thermal damage, or in the case of
\par UV treatment, absorbing the UV light itself.
\par
\par Organic compounds
\par
\par Water can be contaminated by a number of organic compound such as
\par chloroform, gasoline, pesticides, and herbicides. These contaminants
\par must be identified in a lab test. It is unlikely ground water will
\par suddenly become contaminated unless a quantity of chemicals is allowed
\par to enter a well or penetrating the aquifer. One exception is when the
\par aquifer is located in limestone. Not only will water flow faster
\par through limestone, but the rock is prone to forming vertical channels or
\par sinkholes that will rapidly allow contamination from surface water.
\par Surface water may show great swings in chemical levels due to
\par differences in rainfall, seasonal crop cultivation, and industrial
\par effluent levels
\par
\par
\par -Pathogens-
\par Protozoa
\par
\par Protozoa cysts are the largest pathogens in drinking water, and are
\par responsible for many of the waterborne disease cases in the US.
\par Protozoa cysts range is size from 2 to 15 microns (a micron is one
\par millionth of a meter), but can squeeze through smaller openings. In
\par order to insure cyst filtration, filters with a absolute pore size of
\par 1 micron or less should be used. The two most common protozoa pathogens
\par are Giardia lamblia (Giardia) and Cryptosporidium (Crypto). Both
\par organisms have caused numerous deaths in recent years in the US, the
\par deaths occurring in the young and elderly, and the sick and immune
\par compromised. Many deaths were a result of more than one of these
\par conditions. Neither disease is likely to be fatal to a healthy adult,
\par even if untreated. For example in Milwaukee in April of 1993, of 400,000
\par who were diagnosed with Crypto, only 54 deaths were linked to the
\par outbreak, 84% of whom were AIDS patients. Outside of the US and other
\par developed countries, protozoa are responsible for many cases of amoebic
\par dysentery, but so far this has not been a problem in the US, due to
\par better wastewater treatment. This could change during a survival
\par situation. Tests have found Giardia and/or Crypto in up to 5% of
\par vertical wells and 26% of springs in the US.
\par
\par Bacteria
\par
\par Bacteria are smaller than protozoa and are responsible for many diseases
\par such as typhoid fever, cholera, diarrhea, and dysentery. Pathogenic
\par bacteria range in size from 0.2 to 0.6 microns, and a 0.2 micron filter
\par is necessary to prevent transmission. Contamination of water supplies
\par by bacteria is blamed for the cholera epidemics which devastate
\par undeveloped countries from time to time. Even in the US, E. coli is
\par frequently found to contaminate water supplies. Fortunately E. coli is
\par relatively harmless as pathogens go, and the problem isn't so much with
\par E. coli found, but the fear that other bacteria may have contaminated
\par the water as well. Never the less, dehydration from diarrhea caused by
\par E. coli has resulted in fatalities.
\par
\par Viruses
\par
\par Viruses are the 2nd most problematic pathogen, behind protozoa. As with
\par protozoa, most waterborne viral diseases don't present a lethal hazard
\par to a healthy adult. Waterborne pathogenic viruses range in size from
\par 0.020-0.030 microns, and are too small to be filtered out by a
\par mechanical filter. All waterborne enteric viruses affecting humans
\par occur solely in humans, thus animal waste doesn't present much of a
\par viral threat. At the present viruses don't present a major hazard to
\par people drinking surface water in the US, but this could change in a
\par survival situation as the level of human sanitation is reduced. Viruses
\par do tend to show up even in remote areas, so case can be made for
\par eliminating them now.
\par
\par
\par Physical Treatment
\par
\par Heat Treatment
\par
\par Boiling is one guaranteed way to purify water of all pathogens. Most
\par experts feel that if the water reaches a rolling boil it is safe. A few
\par still hold out for maintaining the boiling for some length of time,
\par commonly 5 or 10 minutes, plus an extra minute for every 1000 feet of
\par elevation. If one wishes to do this, a pressure cooker would allow the
\par water to be kept at boiling with out loosing the heat to evaporation.
\par One reason for the long period of boiling may be to inactivate bacterial
\par spores (which can survive boiling), but these spore are unlikely to be
\par waterborne pathogens.
\par
\par African aid agencies figure it takes 1 kg of wood to boil 1 liter of
\par water. Hardwoods and efficient stoves would improve on this.
\par
\par Water can also be treated at below boiling temperatures, if contact time
\par is increased. A commercial unit has been developed that treats 500 gals
\par of water per day at an estimated cost of $1/1000 gallons for the energy.
\par The process is similar to milk pasteurization, and holds the water at
\par 161 deg F for 15 seconds. Heat exchangers recover most of the energy
\par used to warm the water. Solar pasteurizers have also been built that
\par would heat three gallons of water to 65deg C and hold the temperature
\par for an hour. A higher temperature could be reached if the device was
\par rotated east to west during the day to follow the sunlight.
\par
\par Regardless of the method, heat treatment does not leave any form of
\par residual to keep the water free of pathogens in storage.
\par
\par Reverse Osmosis.
\par
\par Reverse osmosis forces water, under pressure, through a membrane that is
\par impermeable to most contaminants. The most common use is aboard boats
\par to produce fresh water from salt water. The membrane is somewhat better
\par at rejecting salts than it is at rejecting non-ionized weak acids and
\par bases and smaller organic molecules (molecular weight below 200). In
\par the latter category are undissociated weak organic acids, amines,
\par phenols, chlorinated hydrocarbons, some pesticides and low molecular
\par weight alcohols. Larger organic molecules, and all pathogens are
\par rejected. Of course it is possible to have a imperfection in the
\par membrane that could allow molecules or whole pathogens to pass through.
\par
\par Using reverse osmosis to desalinate seawater requires considerable
\par pressure (1000 psi) to operate, and for a long time only electric models
\par were available. Competing for a contract to build a hand powered model
\par for the Navy, Recovery Engineering designed a model that could operate
\par by hand, using the waste water (90 percent of the water is waste water,
\par only 10% passes through the filter) to pressurize the back side of the
\par piston. The design was later acquired by PUR. While there is little
\par question that the devices work well, the considerable effort required to
\par operate one has been questioned by some survival experts such as Michael
\par Greenwald, himself a survivor of a shipwreck. On the other hand the
\par people who have actually used them on a life raft credit the
\par availability of water from their PUR watermaker for their survival.
\par
\par PUR manual watermakers are available in two models:
\par
\par The Survivor 06 ($500) produces 2 pints per hour, and
\par
\par The Survivor 35 ($1350) produces 1.4 gal/hr. The latter model is also
\par available as the Power Survivor 35 ($1700), which produces the same
\par water volume from 4 Amps of 12 VDC, and can be disconnected and used as
\par a hand held unit.
\par
\par A number of manufactures, including PUR, make DC powered models for
\par shipboard use. PUR recommends replacing the O rings every 600 hours on
\par its handheld units, and a kit is available to do this. Estimates for
\par membrane life vary, but units designed for production use may last a
\par year or more. Every precaution should be taken to prevent petroleum
\par products from contacting the membrane as they will damage or destroy the
\par membrane. The prefilter must also be regularly changed, and the membrane
\par may need to be treated with a biocide occasionally
\par
\par Reverse osmosis filter are also available that will use normal municipal
\par or private water pressure to remove contaminates from water, as long as
\par they aren't present in the levels found in sea water.
\par
\par The water produced by reverse osmosis, like distilled water, will be
\par close to pure H2O. Therefore mineral intake may need to be increased to
\par compensate for the normal mineral content of water in much of the world.
\par
\par Distillation
\par
\par Distillation is the evaporation and condensation of water to purify
\par water. Distillation has two disadvantages:
\par
\par 1) A large energy input is required and
\par 2) If simple distillation is used, chemical contaminants with boiling
\par points below water will be condensed along with the water.
\par
\par Distillation is most commonly used to remove dissolved minerals and
\par salts from water.
\par
\par The simplest form of a distillation is a solar still. A solar still
\par uses solar radiation to evaporate water below the boiling point, and the
\par cooler ambient air to condense the vapor. The water can be extracted
\par from the soil, vegetation piled in the still, or contaminated water
\par (such as radiator fluid or salt water) can be added to the still. While
\par per still output is low, they are an important technique if water is in
\par short supply
\par
\par Other forms of distillation require a concentrated heat source to boil
\par water which is then condensed. Simple stills use a coiling coil to
\par return this heat to the environment. These can be improvised with a
\par boiler and tight fitting lid and some copper tubing (Avoid using lead
\par soldered tubing if possible). FEMA suggests that, in an emergency, a
\par hand towel can be used to collect steam above a container of boiling
\par water. More efficient distillations plants use a vapor compression
\par cycle where the water is boiled off at atmospheric pressure, the steam
\par is compressed, and the condenser condenses the steam above the boiling
\par point of the water in the boiler, returning the heat of fusion to the
\par boiling water. The hot condensed water is run through a second heat
\par exchanger which heats up the water feeding into the boiler. These
\par plants normally use an internal combustion engine to run the compressor.
\par Waste heat from the engine, including the exhaust, is used to start the
\par process and make up any heat loss. This is the method used in most
\par commercial and military desalinization plants
\par
\par Inflatable solar stills are available from marine supply stores, but
\par avoid the WW2 surplus models, as those who have used them have had a
\par extremely high failure rate. Even new inflatable solar stills may only
\par produce from 30-16 oz under actual conditions, compared to a rating of
\par 48 oz/day under optimum conditions.
\par
\par Jade Mountain also offers the following portable models in travel cases:
\par
\par Traveler (WC106)\tab 1 gpd, 23 lb., 24x26x10 folded\tab $ 695
\par
\par Base Camp (WC107) 2 gpd, 51 lb., 48x48x4 folded $ 895
\par
\par Safari (WC108) 48x48x5 $1095
\par \tab A ruggedized version of the Base Camp above
\par
\par
\par Microfilters
\par
\par Microfilters are small-scale filters designed to remove cysts, suspended
\par solids, protozoa, and in some cases bacteria from water. Most filters
\par use a ceramic or fiber element that can be cleaned to restore
\par performance as the units are used. Most units and almost all made for
\par camping use a hand pump to force the water through the filter. Others
\par use gravity, either by placing the water to be filtered above the filter
\par (e.g. the Katadyn drip filter), or by placing the filter in the water,
\par and running a siphon hose to a collection vessel located below the
\par filter (e.g. Katadyn siphon filter). Microfilters are the only method,
\par other than boiling, to remove Cryptosporidia. Microfilters do not
\par remove viruses, which many experts do not consider to be a problem in
\par North America. Despite this the Katadyn microfilter has seen
\par considerable use around the world by NATO-member militaries, WHO, UNHCR,
\par and other aid organizations. Microfilters share a problem with charcoal
\par filter in having bacteria grow on the filter medium. Some handle this
\par by impregnating the filter element with silver such as the Katadyn,
\par others advise against storage of a filter element after it has been
\par used. The Sweetwater Guardian suggests using a freezer for short-term
\par storage
\par
\par Many microfilters may include silt prefilters, activated charcoal
\par stages, or an iodine resin. Most filters come with a stainless steel
\par prefilter, but other purchased or improvised filters can be added to
\par reduce the loading on the main filter element. Allowing time for solids
\par to settle, and/or prefiltering with a coffee filter will also extend
\par filter life. Iodine matrix filters will kill viruses that will pass
\par through the filter, and if a charcoal stage is used it will remove much
\par of the iodine from the water. Charcoal filters will also remove other
\par dissolved natural or manmade contaminates. Both the iodine and the
\par charcoal stages do not indicate when they reach their useful life, which
\par is much shorter than the filter element. If you are depending on the
\par stage for filtering the water you will have to keep up with how much
\par water passes through it.
\par
\par New designs seem to be coming out every month. The best selling brands
\par seem to be the PUR, and Sweetwater Guardian. The Katadyn doesn't sell
\par as well to outdoor enthusiasts due to its high cost, but for years it
\par was state of the art for water purification and still has a loyal
\par following, especially among professionals in relief work. Below is the
\par data on a few of the more common units, for a excellent field test of
\par some common units, see the December 96 issue of Backpacker magazine.
\par
\par Note that the first price is for the filter, the second for the
\par replacement filter. The weight is from manufacturer's literature if it
\par was not listed in the Backpacker article. Filter life is from
\par manufacturer\rquote s literature and should be taken with a grain of salt.
\par
\par Basic Designs Ceramic Filter Pump ($29/$15, 8 oz.) Cheap flimsy filter,
\par claimed to filter up to 500 gallons with a 0.9 micron ceramic filter.
\par Not EPA rated, may not have passed independent lab tests, prone to
\par damage, filter element must be submerged in water.
\par
\par General Ecology- First Need Deluxe ($70/$30, 20 oz) This filter uses a
\par structured matrix micro strainer, though General Ecology won't reveal
\par what the structure is. It has survived independent lab tests, and
\par filters particles to .4 microns, while actually removing viruses (the
\par only filter capable of doing this) through electrostatic attraction.
\par The filter cartridges can't be cleaned (other than by back flushing),
\par but are good for 100 gallons. Pump design isn't the best. Other models
\par are available from the manufacturer.
\par
\par Katadyn PF ($295/$145, 22.7 oz). The original microfilter using a 0.2
\par micron silver impregnated ceramic candle. An extremely thick filter
\par allows it to be cleaned many times for up to 14,000 gallons capacity.
\par While the Katadyn seems well made, one reader of this list reported
\par breaking the candle, and Backpacker Magazine broke the case during a
\par field test. The pump, while probably indestructible, is somewhat slow
\par and hard to use, requiring 20 lbs. of force on a small handle. The PF
\par also lacks a output hose as the Katadyn engineers felt if would be a
\par source of contamination.
\par
\par Katadyn Combi ($185/$75 (ceramic)/$19 (carbon), 29 oz) A cheaper version
\par of the PF incorporating both ceramic and carbon stages. Much faster
\par filter than the PF.
\par
\par Katadyn Minifilter ($139/$59, 8.3 oz) A smaller and cheaper version of
\par the PF, easier to pump, but generally not well received. Good for 200
\par gallons.
\par
\par Katadyn Expedition ($680/$77, 13 lb.) Similar filter to the PF (exact
\par same cartridge as the Drip Filter Below), but designed for much higher
\par production, stainless steel case with spade type D handle, produces 0.75
\par gpm. Filter good for 26,000 gallons.
\par
\par Katadyn Drip Style Filter ($240, $77, 12.5 lb.) Filter elements similar
\par to those in the PF are mounted vertically in top 3 gallon plastic
\par bucket, water drips through filters into second 3 gallon bucket with
\par faucet. 1 qt, per hour with the 2 filters included, a third filter can
\par be added to increase rate 50%. Each filter good for 13,000 gallons.
\par The mounting hardware for the filters is available for $10 to allow you
\par to make your own filter of what ever size is needed. Each mounting kit
\par requires a \'bd\rdblquote hole in the bottom of the raw water container.
\par
\par Katadyn Siphon Filter ($92, 2 lb.) Similar design to PF filter element,
\par but a siphon hose replaces the pump, filters 1-2 quarts per hour (allow
\par 1 hour for the filter to "prime" itself via capillary action), but
\par multiple filters can be used in the same container. Collection vessel
\par must be lower than raw water container. Good for 13,000 gallons.
\par
\par MSR Miniworks ($59/$30, 14 oz) MSR's smaller filter, using a 0.3 micron
\par ceramic element. Pump is well designed, and easy to use. Main drawback
\par is that the clean water discharge is from the bottom of the filter, and
\par no hose is provided. While the bottom is threaded for a Nalgene bottle,
\par it is a pain in the butt to fill a canteen or 2 liter bottle. Claimed
\par to filter 100 gallons, Backpacker Magazine feels this may be one of the
\par few filters without a grossly inflated rating
\par
\par MSR Waterworks ($140/$30/$30, 17 oz) MSR's first filter with a 0.2
\par micron ceramic and membrane stage and a carbon stage. Other wise
\par similar to the Miniworks.
\par
\par PUR Pioneer ($30/$4, 8 oz), newly introduced low-end microfilter. 0.5
\par micron, 1 lpm filter rate, 12 gallon capacity
\par
\par PUR Hiker ($50/$20, 12 oz) PUR's microfilter only design, filters to .5
\par micron. Well liked, as are the other PUR filters. Very compact. 200
\par gallon capacity
\par
\par PUR Scout ($70/$35/$15, 12 oz) Combines a iodine resin stage, a 1.0
\par micron filter, and a activated charcoal filter. 200 gallon capacity
\par
\par PUR Explorer ($130/$45, 22 oz) PUR's top of the line model. Bulky, but
\par well made, with a high output (1.4 lpm, faster than any of the hand
\par held models listed and one of the easiest to pump) Has a 1.0 micron
\par filter plus a iodine resin stage, 300 gallon capacity
\par
\par Sweetwater Walkabout($35/$13, 8.5 oz.) Sweetwater's low end filter, 0.2
\par micron, .7 lpm, 100 gal capacity
\par
\par Sweetwater Guardian ($60/$20, 11 oz) Uses a glass fiber and carbon
\par filter, filters to .2 micron, claimed to last for 200 gallons. An
\par iodine resin stage can be added that will kill viruses, and will last
\par for 90 gallons. Pump is well designed, but it takes a few seconds to
\par pull a captive pin to fold for storage. Available in white or OD.
\par
\par Timberline Eagle ($20/$13, 8 oz) At 1 micron, this filter only does
\par protozoa, but is much easier to pump, lighter, and cheaper. Filter is
\par attached to pump, and must rest (but doesn't have to be submerged) in
\par water to be purified. Looks flimsy, but seems to hold up. Claimed to
\par last for 100 gallons.
\par
\par It is also possible to build your own microfilter using diatomaceous
\par earth, sold for swimming pool filters (DE). Usually pressure is
\par required to achieve a reasonable flow rate. A DE filter will remove
\par turbidity as well as pathogens larger than 1 micron.
\par
\par
\par Slow Sand Filter
\par
\par Slow sand filters pass water slowly through a bed of sand. Pathogens
\par and turbidity are removed by natural die-off, biological action, and
\par filtering. Typically the filter will consist of 24 inches of sand, then
\par a gravel layer in which the drain pipe is embedded. The gravel doesn't
\par touch the walls of the filter so that water can't run quickly down the
\par wall of the filter and into the gravel. Building the walls with a rough
\par surface also helps. A typical loading rate for the filter is 0.2
\par meters/hour day (the same as .2 m^3/m^2 of surface area). The filter
\par can be cleaned several times before the sand has to be replaced.
\par
\par Slow sand filter construction information: Slow sand filters should
\par only be used for continuous water treatment. If a continuous supply of
\par raw water can't be insured (say using a holding tank), then another
\par method should be chosen. It is also important for the water to have as
\par low turbidity (suspended solids) as possible. Turbidity can be reduced
\par by changing the method of collection (for example, building an
\par infiltration gallery, rather than taking water directly from a creek),
\par allowing time for the material to settle out (using a raw water tank),
\par prefiltering or flocculation (adding a chemical such as alum to cause
\par the suspended material to floc together.)
\par
\par The SSF filter itself is a large box, at least 1.5 meters high. The
\par walls should be as rough as possible to reduce the tendency for water to
\par run down the walls of the filter, bypassing the sand. The bottom layer
\par of the filter is a gravel bed in which a slotted pipe is placed to drain
\par off the filtered water. The slots or the gravel should be no closer
\par than 20 cm to the walls. again to prevent the water from bypassing the
\par sand.
\par
\par The sand for a SSF needs to be clean and uniform, and of the correct
\par size. The sand can be cleaned in clean running water , even if it is in
\par a creek. The ideal specs on sand are effective size (sieve size through
\par which 10% of the sand passes) between 0.15 and 0.35 mm, uniformity
\par coefficient (ratio of sieve sizes through which 60% pass and through
\par which 10% pass) of less than 3, Maximum size of 3 mm, and minimum size
\par of 0.1 mm.
\par
\par The sand is added to a SSF to a minimum depth of 0.6 meters. Additional
\par thickness will allow more cleanings before the sand must be replaced.
\par 0.3 to 0.5 meters of extra sand will allow the filter to work for 3-4
\par years. An improved design uses a geotextile layer on top of the sand to
\par reduce the frequency of cleaning. The outlet of a SSF must be above the
\par sand level, and below the water level. The water must be maintained at
\par a constant level to insure an even flow rate throughout the filter. The
\par flow rate can be increased by lowering the outlet pipe, or increasing
\par the water level. One common idea for maintaining the water level is to
\par use a elevated raw water tank or pump, and a ball valve from a toilet.
\par
\par While the SSF will begin to work at once, optimum treatment for
\par pathogens will take a week or more. During this time the water should
\par be chlorinated if at all possible (iodine can be substituted). After
\par the filter has stabilized, the water should be safe to drink, but
\par chlorinating of the output is still a good idea, particularly to prevent
\par recontamination.
\par
\par As the flow rate slows down the filter will have to be cleaned by
\par draining and removing the top few inches of sand. If a geotextile
\par filter is used, only the top \'bd\rdblquote may have to be removed. As the filter
\par is refilled, it will take a few days for the biological processes to
\par reestablish themselves.
\par
\par
\par Activated Charcoal Filter
\par
\par Activated charcoal filters water through adsorption, chemicals and some
\par heavy metals are attracted to the surface of the charcoal, and are
\par attached to it. Charcoal filters will filter some pathogens though they
\par will quickly use up the filter adsorptive ability, and can even
\par contribute to contamination as the charcoal provides an excellent
\par breeding ground for bacteria and algae. Some charcoal filters are
\par available impregnated with silver to prevent this, though current
\par research concludes that the bacteria growing on the filter are harmless,
\par even if the water wasn't disinfected before contacting the filter. The
\par only filter I know of that uses only activated charcoal, and doesn't
\par required pressurized water is the Water Washer ($59). Available from
\par the Survival Center.
\par
\par Activated charcoal can be used in conjunction with chemical treatment.
\par The chemical (iodine or chlorine) will kill the pathogens, while the
\par carbon filter will remove the treatment chemicals. In this case, as the
\par filter reaches its capacity, a distinctive chlorine or iodine taste will
\par be noted.
\par
\par Activated charcoal can be made at home, though the product will be of
\par varying quality compared to commercial products. Either purchased or
\par homemade charcoal can be recycled by burning off the molecules adsorbed
\par by the carbon (The won't work with heavy metals of course.)
\par
\par The more activated charcoal in a filter, the longer it will last. The
\par bed of carbon must be deep enough for adequate contact with the water.
\par Production designs use granulated activated charcoal (effective size or
\par 0.6 to 0.9 mm for maximum flow rate. Home or field models can also use
\par a compressed carbon block or powered activated charcoal (effective size
\par 0.01) to increase contact area. Powered charcoal can also be mixed with
\par water and filtered out later. As far as life of the filter is
\par concerned, carbon block filters will last the longest for a given size,
\par simply due to their greater mass of carbon. A source of pressure is
\par usually needed with carbon block filters to achieve a reasonable flow
\par rate.
\par
\par
\par Sol-Air Water Treatment
\par
\par If sufficient dissolved oxygen is available, sunlight will cause the
\par temporary formation of reactive forms of oxygen such as hydrogen
\par peroxide and oxygen free radicals. This form of water treatment is
\par called solar photooxidative disinfection or sol-air water treatment.
\par Sol-Air water treatment has been shown to dramatically reduce the level
\par of fecal coliform bacteria. There is some evidence that other bacteria
\par and viruses may be affected also. While not as reliable as other
\par methods, it does offer a low-tech solution in emergencies. Sol-Air
\par treatment requires bright sunlight, and has been shown to be effective
\par when ever the sun causes a distinct shadow to be cast. Exposure to 4.5
\par hours of bright sunlight has been shown to cause a thousand fold
\par reduction in fecal coliforms in lab tests
\par
\par In order for Sol-Air to be effective, oxygen must be present.
\par Experiments have shown that shaking a bottle filled 3/4 with air will
\par restore oxygen levels to near saturation. As the treatment continues,
\par some of the oxygen will come out of solution, while other oxygen will be
\par consumed by the killed pathogens, so the shaking should be repeated
\par every few hours. Data shows that maximum activity occurs when the water
\par temperature is above 50deg C (122deg F), so this method may be
\par unsuitable in colder climates unless special solar collectors are used.
\par
\par Either glass or plastic bottles may be used. Plastic bottles will allow
\par short wave ultraviolet radiation to pass, increasing the rate of
\par microbial inactivation, but may yellow with age, reducing light
\par transmission, and may leach plasticizers into the water at the elevated
\par temperatures that will occur. The leaching of plasticizers can be
\par reduced by using bottles of PET (polyethlyene terephtalate) rather than
\par PVC. Glass bottles on the other hand are more durable. Research has
\par used bottles with 2 liters of capacity, but if the water is free of
\par turbidity, larger containers can be used. Plastic bags, or some sort of
\par flat glass container represent the ideal container as this maximizes the
\par solar energy received per ounce of water.
\par
\par Bottles should be filed 3/4 full in the early morning with water as free
\par of turbidity as possible. After capping the bottles should be shaken
\par vigorously for a few minutes then placed upright in the sun, where they
\par will be not be shaded later in the day. The shaking should be repeated
\par at least three times during the day. At the end of the day the water
\par should be reasonably freed of bacteria, though it is most practical to
\par let the water cool for consumption the following day. Each day a new
\par batch should be treated due to the lack of a residual disinfected.
\par
\par After consumption of the water the bottle should be air dried to prevent
\par algae growth with continual use.
\par
\par
\par Improvised Mechanical Filter
\par
\par If the materials aren\rquote t available to build a slow sand filter, or some
\par other means of water treatment is preferred, it may still be
\par advantageous to mechanically filter the water before treating it with
\par chemicals or passing through a microfilter. Generally the idea is to
\par allow the water to flow as slowly as possible through a bed of sand. In
\par a municipal water treatment plant this is called a rapid sand filter.
\par The particular design below is included, because the designer, a
\par research engineer at Oak Ridge National Laboratories, found it
\par particularly effective at removing fallout from water. The filter will
\par do little or nothing to remove pathogens, though removing suspended
\par solids allow others water treatment methods to work more effectively.
\par
\par
\par Expedient water filter, from Nuclear War Survival Skills, Cresson
\par Kearny, ORNL
\par
\par 1) Perforate the bottom of a 5 gallon bucket, or similar container with
\par a dozen nail holes even spread over a 4" diameter circle in the center
\par of the container.
\par
\par 2) Place a 1.5" layer of small stones or pebbles in the bottom of the
\par can. If pebbles aren\rquote t available, marbles, clean bottle caps, twisted
\par coat hangers or clean twigs can be used.
\par
\par 3) Cover the pebbles with one thickness of terrycloth towel, burlap
\par sackcloth, or other porous cloth. Curl the cloth in a roughly circular
\par shape about three inches larger then the diameter of the can.
\par
\par 4) Take soil containing some clay (pure clay isn't porous enough, pure
\par sand is too porous) from at least 4\rdblquote below the surface of the ground
\par (nearly all fallout particles remain near the surface except after
\par disposition on sand or gravel.)
\par
\par 5) Pulverize the soil, then gently press it in layers over the cloth
\par that covers the pebbles, so that the cloth is held snugly against the
\par walls of the can. The soil should be 6-7" thick.
\par
\par 6) Completely cover the surface of the soil layer with one thickness of
\par fabric as porous as a bath towel. This is to keep the soil from being
\par eroded as water is being poured into the filter. A dozen small stones
\par placed on the cloth near it's edges will secure it adequately.
\par
\par 7) Support the filter on rocks or sticks placed across the top of a
\par container that is larger then the filter can (such as a dishpan)
\par
\par The contaminated water should be poured into the filter can, preferably
\par after allowing it to settle as described below. The filtered water
\par should be disinfected by some method.
\par
\par If the 6 or 7 inches of filtering soil is a sandy clay loam, the filter
\par will initially deliver about 6 quarts/hour. If the filter is any faster
\par than this then the fabric layer needs to be removed and the soil
\par compressed more. The filtering rate will drop over time as the filter
\par begins to clog up. When this happens the top 1/2" of soil can be
\par removed to increase the filtering rate. After 50 or so quarts, the
\par filter will need to be rebuilt with fresh soil.
\par
\par As with any filter, optimum performance will be achieved if sediment in
\par the water will be allowed to settle out before passing the water through
\par the filter
\par
\par If the water is contaminated with fallout, clay can be added to help the
\par fallout particles to settle out. The procedure is as follows:
\par
\par Fill a bucket or other deep container 3/4 full with contaminated water.
\par Dig pulverized clay or clayey soil from a depth of four or more inches
\par below ground surface and stir it into the water. Use about 1 inch of dry
\par clay or clayey soil for every 4" depth of water. Stir until practically
\par all of the clay particles are suspended in the water. Let the clay
\par settle for at least 6 hours. This will carry the fallout particles to
\par the bottom and cover them. Carefully dip out or siphon the clear water
\par and disinfect it.
\par
\par
\par Chemical Treatment
\par
\par Chlorine:
\par
\par Chlorine is familiar to most Americans as it is used to treat virtually
\par all municipal water systems in the United States. For a long time
\par chlorine, in the form of Halazone tablets, was used to purify small
\par batches of water for campers and military troops. Later questions
\par emerged about the effectiveness of Halazone, and in 1989, Abbot labs
\par pulled it off the market. If Halazone tablets are encountered outside
\par the US, the nominal shelf life is 6 months, and the dosage is 2 tabs per
\par liter. Until recently, there was no chlorine product designed for
\par wilderness/survival use available in the US.
\par
\par Chlorine has a number of problems when used for field treatment of
\par water. When chlorine reacts with organic material, it attaches itself
\par to nitrogen containing compounds (ammonium ions and amino acids),
\par leaving less free chlorine to continue disinfection. Carcinogenic
\par trihalomethanes are also produced, though this is only a problem with
\par long-term exposure. Trihalomethanes can also be filtered out with a
\par charcoal filter, though it is more efficient to use the same filter to
\par remove organics before the water is chlorinated. Unless free chlorine
\par is measured, disinfection can not be guaranteed with moderate doses of
\par chlorine. One solution is superchlorination, the addition of far more
\par chlorine than is needed. This must again be filtered through activated
\par charcoal to remove the large amounts of chlorine, or hydrogen peroxide
\par can be added to drive the chlorine off. Either way there is no residual
\par chlorine left to prevent recontamination. This isn't a problem if the
\par water is to be used at once.
\par
\par Chlorine is sensitive to both the pH and temperature of the treated
\par water. Temperature slows the reaction for any chemical treatment, but
\par chlorine treatment is particularly susceptible to variations in the pH
\par as at lower pHs, hypochlorous acid is formed, while at higher pHs, it
\par will tend to dissociate into hydrogen and chlorite ions, which are less
\par effective as a disinfectant. As a result, chlorine effectiveness drops
\par off when the pH is greater than 8
\par
\par Chlorine, like iodine, will not kill Cryptosporidia.
\par
\par Methods of chlorine treatment:
\par
\par Bleach: Ordinary household bleach (such as Clorox) in the US contains
\par 5.25% sodium hypochlorite (NaOCL) and can be used to purify water if it
\par contains no other active ingredients, scents, or colorings. Bleach is
\par far from an ideal source due to its bulkiness (only 5% active
\par ingredient), and the instability over time of the chlorine content in
\par bleach. Chlorine loss is farther increased by agitation or exposure to
\par air. One source claims chlorine loss from a 5% solution at 10% over 6
\par months if stored at 70deg F. Nevertheless, this may be the only
\par chemical means available to purify water, and it is far better than
\par nothing. Normal dosage is 8 drops (0.4 ml) per gallon. Allow the treated
\par water to sit for 30 min., and if there isn't a slight chlorine smell,
\par retreat. Note: USP standard medicine droppers are designed to dispense
\par 0.045-0.055 ml per drop. Use of other solvents or some chemicals can
\par change this. The dropper can be calibrated against a graduated cylinder
\par for greater accuracy.
\par
\par Some small treatment plants in Africa produce their own sodium
\par hypochlorite on site from the electrolysis of brine. Power demands
\par range from 1.7 to 4 kWh per lb. of NaOCL. 2 to 3.5 lbs. of salt are
\par needed for each pound of NaOCL. These units are fairly simple and are
\par made in both the US and the UK. Another system, designed for China,
\par where the suitable raw materials were mined or manufactured locally,
\par used a reaction between salt, manganese dioxide, and sulfuric acid to
\par produce chlorine gas. The gas was then allowed to react with slaked
\par lime to produce a bleaching powder that could then be used to treat
\par water. A heat source is required to speed the reaction up.
\par
\par AquaCure: Designed for the South African military, these tablets
\par contain chlorine and alum. The alum causes the suspended solids to
\par flocculate and the chlorine adds 8 PPM chlorine. This is a great way to
\par treat turbid water, though it will leave a lot of chlorine in clear
\par water (The one tablet/liter could be halved for clear water.)
\par
\par The US distributor for Aqua Cure is:
\par
\par Safesport Manufacturing
\par \tab Box 11811
\par \tab Denver, CO 80211
\par \tab 1 800 433 6506
\par
\par Bleaching Powder (Chlorinated Lime): Can also be purchased and used as
\par a purification means if nothing else is available. Bleaching powder is
\par 33-37% chlorine when produced, but losses its chlorine rapidly,
\par particularly when exposed to air, light or moisture.
\par
\par Calcium Hypochlorite: Also known as High Test Hypochlorite. Supplied
\par in crystal form, it is nearly 70% available chlorine. One product, the
\par Sanitizer (formally the Sierra Water Purifier) uses these crystals to
\par superchlorinate the water to insure pathogens were killed off, then
\par hydrogen peroxide is added to drive off the residual chlorine. This is
\par the most effective method of field chlorine treatment. The US military
\par and most aid agencies also use HTH to treat their water, though a test
\par kit, rather than superchlorination, is used to insure enough chlorine is
\par added. This is preferable for large-scale systems as the residual
\par chlorine will prevent recontamination
\par
\par Usually bulk water treatment plants first dilute to HTH to make a 1%
\par working solution at the rate of 14g HTH per liter of water. While
\par testing to determine exact chlorine needs are preferable, the solution
\par can be used at the dose rate of 8 drops/gallon, or for larger
\par quantities, 1 part of 1% solution to 10,000 parts clear water. Either
\par of these doses will result in 1 PPM chlorine and may need to be
\par increased if the water wasn't already filtered by other means.
\par
\par When test kits are available, the WHO standard is a residual chlorine
\par level of 0.2 to 0.5 mg/l after a 30 min. contact time. The may require
\par as much as 5 mg/l of chlorine to be added to the raw water.
\par
\par
\par Iodine:
\par
\par Iodine's use as a water purification method emerged after WW2, when the
\par US military was looking for a replacement for Halazone tablets. Iodine
\par was found to be in many ways superior to chlorine for use in treating
\par small batches of water. Iodine is less sensitive to the pH and organic
\par content of water, and is effective in lower doses. Some individuals are
\par allergic to iodine, and there is some question about long term use of
\par iodine. The safety of long-term exposure to low levels of iodine was
\par proven when inmates of three Florida prisons were given water
\par disinfected with 0.5 to 1.0 PPM iodine for 15 years. No effects on the
\par health or thyroid function of previously healthy inmates was observed.
\par Of 101 infants born to prisoners drinking the water for 122- 270 days,
\par none showed detectable thyroid enlargement. However 4 individuals with
\par preexisting cases of hyperthyroidism became more symptomatic while
\par consuming the water.
\par
\par Nevertheless experts are reluctant to recommend iodine for long term
\par use. Average American iodine intake is estimated at 0.24 to 0.74
\par mg/day, higher than the RDA of 0.4 mg/day. Due to a recent National
\par Academy of Science recommendation that iodine consumption be reduced to
\par the RDA, the EPA discourages the use of iodized salt in areas where
\par iodine is used to treat drinking water.
\par
\par Iodine is normally used in doses of 8 PPM to treat clear water for a 10
\par minute contact time. The effectiveness of this dose has been shown in
\par numerous studies. Cloudy water needs twice as much iodine or twice as
\par much contact time. In cold water (Below 41deg F or 5deg C) the dose or
\par time must also be doubled. In any case doubling the treatment time will
\par allow the use of half as much iodine
\par
\par These doses are calculated to remove all pathogens (other than
\par cryptosporida) from the water. Of these, giardia cysts are the hardest
\par to kill, and are what requires the high level of iodine. If the cysts
\par are filtered out with a microfilter (any model will do since the cysts
\par are 6 microns), only 0.5 PPM is needed to treat the resulting water .
\par
\par Water treated with iodine can have any objectionable taste removed by
\par treating the water with vitamin C (ascorbic acid), but it must be added
\par after the water has stood for the correct treatment time. Flavored
\par beverages containing vitamin C will accomplish the same thing. Sodium
\par thiosulfate can also be used to combine with free iodine, and either of
\par these chemicals will also help remove the taste of chlorine as well.
\par Usually elemental iodine can't be tasted below 1 PPM, and below 2 PPM
\par the taste isn't objectionable. Iodine ions have an even higher taste
\par threshold of 5 PPM. Note that removing the iodine taste does not reduce
\par the dose of iodine ingested by the body
\par
\par Sources of Iodine:
\par
\par Tincture of Iodine: USP tincture of iodine contains 2% iodine and 2.4%
\par sodium iodide dissolved in 50% ethyl alcohol. For water purification
\par use, the sodium iodide has no purification effect, but contributes to
\par the total iodine dose. Thus it is not a preferred source of iodine, but
\par can be used if other sources are not available. 0.4 cc's (or 8 drops)
\par of USP tincture (2% iodine) added to a liter of water will give the 8
\par mg/l (same as 8 PPM). If the iodine tincture isn't compounded to USP
\par specs, then you will have to calculate an equal dose based on the
\par iodine concentration.
\par
\par Lugol's solution: Contains 5% iodine and 10% potassium iodide. 0.15 cc
\par (3 drops) can be added per liter of water, but 3 times more iodine is
\par consumed compared to sources without iodide.
\par
\par Betadyne (povidone iodine) Some have recommended 8 drops of 10%
\par povidone iodine per liter of water as a water treatment method, claiming
\par that at low concentrations povidone iodine can be regarded as a solution
\par of iodine. One study indicated that at 1:10,000 dilution (2
\par drops/liter), there was 2 PPM iodine, while another study resulted in
\par conflicting results. However, at 8 drops/liter, there is little doubt
\par that there is an antimicrobial effect. The manufacturer hasn't spent
\par the money on testing this product against EPA standard tests, but in
\par other countries it has been sold for use in field water treatment.
\par
\par Kahn-Vassher solution. By adding a sufficient amount of iodine crystals
\par to a small bottle, an almost unlimited supply of saturated iodine
\par solution can be produced. As long as crystals remain in the bottle,
\par the solution is saturated. Concentration of the iodine is dependent of
\par temperature, either condition at ambient temperature can be assumed, or
\par commercial models such as Polar Pure incorporate a liquid crystal
\par thermometer to determine dose
\par
\par One criticism of this method is the chance of decanting iodine crystals
\par into the water being treated. This isn't that much of a problem as
\par iodine is very weakly toxic, but the Polar Pure incorporates a collar
\par into the neck of the bottle to help prevent this. Another disadvantage
\par to this method is that the saturated iodine solution must be kept in
\par glass bottles, and is subject to freezing, but this is hardly an
\par insurmountable problem. Freezing, of course, doesn't affect the
\par crystals.
\par
\par This is the method I use, but I do use the commercial Polar Pure bottle,
\par and refill it as necessary with USP crystals. During a crisis, or
\par extended camping trips I would microfilter the water first, so a much
\par lower dose of iodine is needed.
\par
\par With the Polar Pure bottle, dosage information is provided. Otherwise a
\par 1 oz bottle can be used to carry the solution. The bottle is filled
\par with water after use. At the next use, 1/2 of the supernate (15 cc) is
\par poured off into a liter of water. At 68deg F, this will yield a dose
\par of 9 mg/l. To use this method with a microfilter to get a 0.5 PPM
\par concentration, either large batches of water need to be treated (1/2 oz
\par to 4.5 gallons would be 0.5 PPM), or a TB syringe or medicine dropper
\par can be used to measure doses. A USP medicine dropper should give 20
\par drops per ml.
\par
\par Iodine can also be dissolved in alcohol to make a solution of known
\par concentration. I am not aware of any commercial products, but a
\par pharmacy could compound one for you, or you could do it your self. One
\par suggested formula is 8g iodine/100 cc ethyl alcohol which yields enough
\par solution to disinfect 250 gallons of water. At the rate of 0.1 cc (2
\par drops)/liter to give a concentration of 8 mg/l
\par
\par Tetraglycine hydroperiodide (e.g. Potable Aqua) This is the form of
\par iodine used by the US military for field treatment of water in canteen
\par sized batches. Usual dose in one tablet per quart of water to give a
\par concentration of 8 mg/l. Two tablets are used in cloudy or cold water
\par or contact time is doubled. The major downside of this product is that
\par the product will loose its iodine rapidly when exposed to the air.
\par According to the manufacturer, they have a near indefinite life when
\par sealed in the original bottle, but probably should be discarded within a
\par few months of opening. The tablets will change color from gun metal
\par gray to brown as they lose the iodine, and you should see a brown tint
\par to the water after treating.
\par
\par Iodine Resin Filter: Some commercial microfilters incorporate an iodine
\par resin stage to kill viruses and bacteria, with out putting as much
\par iodine in the water as if it had been added to the raw water. A few
\par products rely exclusively on an iodine resin stage. Downside of these
\par filters are their fragile nature, dependency of effectiveness on flow
\par rate and the inability to identify when they need to be discarded. If
\par you are going to use one where the water is known to be contaminated
\par with viruses, then one of the better known brands such as the PUR or
\par Sweetwater Viraguard is recommended. More than one pass through the
\par filter may be necessary in cold weather.
\par
\par Resins do have the advantage of producing less iodine in the water for
\par the same antimicrobial effect as for the most part, they only release
\par iodine when contacted by a microbe. The downside is that physical
\par contact between the microbe and the resin is needed.
\par
\par
\par Silver:
\par
\par Silver has been suggested by some for water treatment and may still be
\par available outside the US. Its use is currently out of favor due to the
\par EPA's establishment of a 50 ppb MCL (Maximum Contaminate Level) limit
\par on silver in drinking water. This limit is set to avoid argyrosis, a
\par cosmetic blue/gray staining of the skin, eyes, and mucous membranes. As
\par the disease requires a net accumulation of 1 g of silver in the body,
\par one expert calculated that you could drink water treated at 50 ppb for
\par 27 years before accumulating 1 g. Silver has only be proven to be
\par effective against bacteria and protozoan cysts, though it is quite
\par likely also effective against viruses.
\par
\par Silver can be used in the form of a silver salt, commonly silver
\par nitrate, a colloidal suspension, or a bed of metallic silver.
\par Electrolysis can also be used to add metallic silver to a solution
\par
\par Some evidence has suggested that silver deposited on carbon block
\par filters can kill pathogens without adding as much silver to the water .
\par
\par Katadyn markets a silver based water treatment product called Micropur.
\par The manufacturer recommends a 2 hr contact time at a dose of 1 tab per
\par liter and states the product is \ldblquote For the disinfection and storage of
\par clear water. Reliably kills bacterial agents of enteric diseases, but
\par not worm eggs, amoeba, or viruses. Neutral to taste...insure protection
\par against reinfection for 1-6 months.\rdblquote ; The following forms are
\par available:
\par
\par Micropur Tablets\tab MT1 1 tablets/qt\tab 25 gal
\par MT2 1 tablet/5qts 62.5 gal
\par
\par Micropur Fluid\tab MF 75 10 drops/gal\tab 75 gals
\par MF250 " " 250 gals
\par
\par Micropur Crystal\tab MC250\tab 1 packet/gal\tab \tab 250 gal
\par MC 2500 1 spoon/25 gal 2500 gal
\par MC12500 1 spoon/250 gal 12500 gal
\par
\par
\par Potassium Permanganate:
\par
\par Potassium Permanganate is no longer commonly used in the developed world
\par to kill pathogens. It is much weaker than the alternatives, more
\par expensive, and leaves a objectionable pink or brown color. If it must
\par be used, 1 gram per liter would probably be sufficient against bacteria
\par and viruses (no data is available on it effectiveness against protozoan
\par cysts.
\par
\par
\par Hydrogen Peroxide:
\par
\par Hydrogen Peroxide can be used to purify water if nothing else is
\par available. Studies have shown of 99 percent inactivation of poliovirus
\par in 6 hr with 0.3 percent hydrogen peroxide and a 99% inactivation of
\par rhinovirus with a 1.5% solution in 24 minutes. Hydrogen Peroxide is
\par more effective against bacteria, though Fe+2 or Cu+2 needs to be present
\par as a catalyst to get a reasonable concentration-time product.
\par
\par
\par Coagulation/Flocculation agents:
\par
\par While flocculation doesn't kill pathogens, it will reduce their levels
\par along with removing particles that could shield the pathogens from
\par chemical or thermal destruction, and organic matter that could tie up
\par chlorine added for purification. 60-98% of coliform bacteria, 65-99% of
\par viruses, and 60-90% of giardia will be removed from the water, along
\par with organic matter and heavy metals.
\par
\par Some of the advantages of coagulation/flocculation can be obtained by
\par allowing the particles to settle out of the water with time
\par (sedimentation), but it will take a while for them to do so. Adding
\par coagulation chemicals such as alum will increase the rate at which the
\par suspended particles settle out by combining many smaller particles into
\par larger floc which will settle out faster. The usual dose for alum is
\par 10-30 mg/liter of water. This dose must be rapidly mixed with the
\par water, then the water must be agitated for 5 minutes to encourage the
\par particles to form flocs. After this at least 30 minutes of settling
\par time is need for the flocs to fall to the bottom, and them the clear
\par water above the flocs may be poured off. Most of the flocculation agent
\par is removed with the floc, nevertheless some question the safety of
\par using alum due to the toxicity of the aluminum in it. There is little to
\par no scientific evidence to back this up. Virtually all municipal plants
\par in the US dose the water with alum.
\par
\par In bulk water treatment, the alum dose can be varied until the idea dose
\par is found. The needed dose varies with the pH of the water and the size
\par of the particles. Increase turbidity makes the flocs easier to produce
\par not harder, due to the increased number of collisions between particles.
\par
\par
\par Treatments requiring electricity:
\par
\par Ozone:
\par
\par Ozone is used extensively in Europe to purify water. Ozone, a molecule
\par composed of 3 atoms of oxygen rather than two, is formed by exposing air
\par or oxygen to a high voltage electric arc. Ozone is much more effective
\par as a disinfectant than chlorine, but no residual levels of disinfectant
\par exist after ozone turns back into O2. (one source quotes a half life of
\par only 120 minutes in distilled water at 20deg C). Ozone is expected to
\par see increased use in the US as a way to avoid the production of
\par trihalomethanes. While ozone does break down organic molecules,
\par sometimes this can be a disadvantage as ozone treatment can produce
\par higher levels of smaller molecules that provide an energy source for
\par microorganisms. If no residual disinfectant is present (as would happen
\par if ozone were used as the only treatment method), these microorganisms
\par will cause the water quality to deteriorate in storage.
\par
\par Ozone also changes the surface charges of dissolved organics and
\par colloidially suspended particles. This causes microflocculation of the
\par dissolved organics and coagulation of the colloidal particles
\par
\par UV light
\par
\par Ultraviolet light has been known to kill pathogens for a long time. A
\par low pressure mercury bulb emits between 30 to 90 % of its energy at a
\par wave length of 253.7 nm, right in the middle of the UV band. If water
\par is exposed to enough light, pathogens will be killed. The problem is
\par that some pathogens are hundreds of times less sensitive to UV light
\par than others. The least sensitive pathogens to UV are protozoan cysts.
\par Several studies show that Giardia will not be destroyed by many
\par commercial UV treatment units. Fortunately these are the easiest
\par pathogens to filter out with a mechanical filter
\par
\par The efficacy of UV treatment is very dependent on the turbidity of the
\par water. The more opaque the water is, the less light that will be
\par transmitted through it. The treatment units must be run at the designed
\par flow rate to insure sufficient exposure, as well as insure turbulent
\par flow rather than plug flow.
\par
\par Another problem with UV treatment is that the damage done to the
\par pathogens with UV light can be reversed if the water is exposed to
\par visible light (specifically 330-500 nm) through a process known as
\par photoreactivation.
\par
\par UV treatment, like ozone or mechanical filtering leaves no residual
\par component in the water to insure its continued disinfection. Any
\par purchased UV filter should be checked to insure it at least complies
\par with the 1966 HEW standard of 16 mW.s/cm^2 with a maximum water depth
\par of 7.5 cm. ANSI/NSF require 38 mWs/cm^2 for primary water treatment
\par systems. This level was chosen to give better than 3 log (99.9%)
\par inactivation of Bacillus subtillis. This level is of little use against
\par Giardia, and of no use against Crypto.
\par
\par The US EPA explored UV light for small scale water treatment plants and
\par found it compared unfavorably with chlorine due to 1) higher costs, 2)
\par lower reliability, and 3) lack of a residual disinfectant.
\par
\par
\par Questionable or Dangerous methods of water treatment.
\par
\par 1) Aerobic 07: Also sold as Aerobic Oxygen. The company refuses to
\par release the disinfectant. It maybe chlorine dioxide, a well known, if
\par somewhat unstable, disinfectant. The company has shown company
\par sponsored tests showing effectiveness against viruses and bacteria (but
\par not against Giardia). No independent testing has been performed, nor
\par has anybody provided concentration-time data for the product.
\par
\par 2) Survival Straw: This product claims to destroy and eliminate
\par impurities including bacteria, protozoa. fungi, chemicals and heavy
\par metals using a matrix of metal alloy. The manufacturer claims the
\par product\rquote s media meets EPA and FDA specs, which is no indication of the
\par filter's effectiveness. The filter violates a number of laws of physics
\par since it claims that it destroys heavy metals and pathogens without
\par filtering them.
\par
\par
\par
\par }