The days of drinking from a cool, sparkling, mountain stream are over. The U.S. Environmental Protection Agency reckons 90 percent of the world’s fresh water is unfit to drink without first being treated. The World Health Organization claims waterborne gastrointestinal infections cause 80% of all disease, and kill more than 50,000 people every day: over 5000 from diarrhoea and cholera.

UPDATE: This is an article from 2002. Iodine is no longer available in the EU - get the latest advice here.

If you believe you are the exception, think on: up to 50% of all holidaymakers catch diarrhoea and the risks for mountaineers away from civilization are much higher. In most countries most tap water is safe to drink most of the time but once beyond the reach of piped water if you want to stay healthy treat your water before cleaning your teeth never mind drinking your fill.

And clarity is no proof of purity. The dangerous pollutants are invisible to the naked eye and produce a range of illnesses that includes amoebic dysentery, bilharziosis, cholera, cryptosporidiosis, giardiasis and schistosomiasis before moving on to the side effects of chemical contaminants from alachlor (a cancer inducing herbicide runoff) to zinc. So what can be done? Polluted water can be made fit to drink in three ways. It can be boiled, treated with chemicals or filtered. The method you choose depends on what is to hand, including cash, how often you need to treat water and the amount of water you need to treat.

Boiling
Boiling is simple and effective. Filter out any sediment before boiling and a rolling boil for at least 1 minute kills protozoan parasites and most bacterial and viral pathogens. The resulting flat taste is disguised by pouring back and forth between a couple of containers. If boiling is your chosen treatment remember that backpacking restricts the amount of fuel carried and don’t forget that adding one minute of boiling to the initial boil for every 1000 feet above sea level eats into your fuel supplies. Boiling does not neutralize chemical pollutants.

Chemical Treatments
Chemical treatment works best if the water temperature is at least 16°C and its ultimate effectiveness depends not only on the temperature, but the pH, and cloudiness of the water. If water is visibly dirty, filter it before beginning treatment. Add the chemicals and let them stand for half an hour for them to do their work; for water temperatures below 10°C wait for at least an hour. Very turbid or very cold water may need to stand for several hours or even overnight. With unfavourable water conditions iodine is better than chlorine. The chemical after taste is reduced by adding a pinch of Vitamin C, or salt, or powdered fruit drinks. If you are using a branded chemical treatment system follow the instructions on the packet but generic chemicals are just as effective and cheaper. Chemicals are a useful way of treating substantial amounts of water but are not always effective against all pollutants.

FILTERS
Filters are either adsorption filters of silver-lmpregnated carbon, charcoal, activated carbon, or ceramics, or membrane filters of thin sheets of precisely sized pores. The effectiveness of any filter depends upon its pore size. Some filters can be cleaned which reduces the frequency they are replaced, others are used until exhausted and then thrown away.

SILVER-IMPREGNATED CARBON OR CHARCOAL FILTERS
Ordinary or silver-impregnated carbon or charcoal filters removes undesirable chemicals, odours, and very large particles, but not micro-organisms.

ACTIVATED CARBON FILTERS
Activated carbon filters have a matrix of millions of microscopic pores and crevices. The pores trap microscopic particles and large organic molecules, while the activated surface areas cling to, or adsorb, small organic molecules. Their ability to eliminate a range of organic chemicals, heavy metals and some bacteria depends upon:

- The type of carbon and the amount used.
- The water flow rate (contact time).
- How long the filter has been in use.
- The impurities the filter has previously removed.
- Water conditions (turbidity, temperature, etc).

Activated carbon is either in grains or solid blocks. Granular activated carbon removes nearly all organic impurities and some bacteria but, ultimately, the impurities accumulating in the filter encourage the growth of bacteria inside the filter. Too many variables make predicting when this starts impossible. Because the carbon grains are held (relatively) loosely pumping water through the filter pushes the granules to one side, opening pathways through the filter, which increases the flow rate and reduces the contact time. This is called channelling.
Solid block filters are made by compressing very fine pulverized activated carbon with a binding medium. They do not suffer from channelling or allow the growth of bacteria inside the filter but as some of the adsorption surface is inert binding agent, and because they tend to clog they have, size for size, less capacity than granular activated carbon filters.
Some filters rely on chemicals like iodide-impregnated resins to destroy the micro organisms as the water flows through the filter. Although this kills many species of bacteria and viruses remember:

- Chemical treatment to remove protozoa is not always effective.
- The contact time for effective treatment varies and may exceed the time the water takes to pass through the filter.
- Chemical filters are not recommended for muddy or very turbid water.
- There is usually no indication to the user when the disinfectant element is depleted.

MEMBRANE FILTERS
Membrane filters transpose the flow of water in the natural process of osmosis so that water passes from a concentrated to a dilute solution through a semi-permeable membrane. Treated water emerges from one side of the membrane, and the accumulated impurities are washed away on the other. This is reverse osmosis or ultrafiltration and because it removes 98% of salts and makes seawater drinkable such systems are sometimes called watermakers.

WATER PURIFIERS
A water filter is not necessarily a water purifier. Filters do not remove viruses, water purifiers do. The United States Environmental Protection Agency defines water purifiers as units which remove, kill or inactivate all types of disease-causing micro-organisms from the water, including bacteria, viruses and protozoan cysts so as to render the processed water safe for drinking. Meeting EPA requirements means a purifier must remove 99.9999% of waterborne bacteria, 99.9% of protozoa, and inactivate 99.99% of viruses. This is tested in different water conditions, including “worst-case”, cold, acidic, and turbid water. Water purifiers need true micro filters, which are:

- Filters in reverse osmosis systems.
- Filters that meet the US National Sanitation Foundation (NSF) Standard 53 for “cyst removal”.
- Filters that have “absolute” 1 micron filters. The “nominal” 1 micron filter rating is not standardized and many “nominal” 1micron filters do not meet the NSF standard.

Most purifiers combine filtration with ultraviolet irradiation, (you need power for this) halogenated resins, or chemical disinfection either alone, or in some combination to offer a very high level of protection. Purifiers are the choice of people who want safe water supplies.

Choosing a system
It is a hard choice. There is a huge range of products on the market and they all claim to be the best at what they do, so before buying decide exactly what you expect of your filter system. The choice begins with silver-impregnated carbon or charcoal filters and moves through various combinations of filters and chemical treatments, up to water purifiers with your wallet emptying in inverse proportion to filter pore size. Remember to check the cost of replacement filters and chemicals. Depending on the type of filter the price of replacements filters can vary between a third and three quarters of the original purchase price.

The next task is to find the model that best suits the environment in which it will operate. Basically the choice is between back packing and base camp systems. The first are small, light, easily carried and aimed at individual use, the latter for the heavier demands of a static base camp.
There is a wide range of back packing filters. Sports-Bottle Filters are new and not easy to find but they are beginning to generate interest. Because they are little more than a filter stuck in a modified sports-bottle, they don’t require the heavy housing of a pump. This keeps the weight down but the filter pore size of the sports-bottle filters is 5 to 10 times larger than pump filters. Some models contain an activated carbon filter, an iodine impregnated resin and a micro-filter and claim to offer complete protection. Others are not all that effective against bacteria and viruses. Sports-bottle filters may provide a convenient solution for people who would like quick treatment of water at a stream away from camp.

Most manufacturers produce at least one high capacity pumped filter system suitable for base camp use. A variation is British Berkfield range of gravity fed systems which use Supersterasyl ceramic filter elements and look rather like a two part tea urn with the filter in the upper section which is filled with dirty water and pure water coming out of a tap on the bottom half. Each filter has a capacity of over 1500 gallons before it needs replacing and produces four gallons of pure water a day. The smallest model is the Arctic Travel Pure SST -1 with a single filter and runs up to SS4 and Big Berkey models which use four filters and turns out almost 20 gallons of drinking water a day.

Before parting with cash satisfy yourself that your chosen system does what it says on the label. A manufacturer’s natural enthusiasm for his product may blind you to its drawbacks. What you need is independent advice. NSF International certification programmes do not recommend, rate, or compare products but test and verify that products are up to standard and that the manufacturers’ claims about their performance are true. NSF testing programmes are recognized worldwide and involve annual inspection and periodic product re-testing. On the NSF website click on Certified Products and then Drinking Water Treatment Units for a long Iist of products which have been certified by the NSF .

If all else fails happy sailors claim a mixture of one part red wine and three parts water makes the water safe to drink. It is something to do with phenol compounds enhanced from contact with the charred wood of the wine aging casks. Columbus, and others, swore by this method but it may just be a waste of good wine.
Who knows? Cheers!

What's safe?

- In most countries regular filtered tap water is safe for older children and adults.

- As is boiled water and chemically treated water.

- As a rule hot tea and coffee are safe. Even if the water has not boiled, heating water is similar to pasteurising it, and most, if not all, harmful bacteria, parasites, and viruses will be eliminated. But be sure the cup is clean.

- Commercially bottled or canned beverages, carbonated water, soft drinks, fruit juices. and beer, are usually heat treated and filtered in the factory, and so are OK.

- Bottled water is not safe to drink in all countries. The origin, the quality, and treatment of bottled water varies, even among brands from the same company and labelling does not always identify low risk products. Claims of well water, artesian well water, spring water or mineral water are no guarantee of purity. Locally bottled water sometimes comes from the nearest tap despite claims on the label. Water from a well or spring free from surface water contamination is less likely to be polluted than water from rivers and lakes.

Common pollutants

Protozoan Parasites are single celled parasitic cysts. Best known are Giardia intestinalis, and Cryptosporidium parvum, found in 90% of U.S. surface water. Giardiasis ranks in the top 20 of killer infectious diseases in Africa, Asia, and Latin America. By micro-organism standards protozoa are large ranging between 1-16 microns (1 micron = 1 millionth of a metre: under 50 microns is invisible to the naked eye.) They can be filtered out of water but are resistant to chemical treatment.

Bacteria range from 0.2 to 1.5 microns and include E. coli, (the cause of 40% of travellers’ diarrhoea) dysentery, cholera, typhoid and Salmonella. Bacteria are caught by some filters and respond well to chemical treatment.

Viruses. The most common illness-causing viruses are the NolWalk and Rotaviruses. Others include polio (0.020 microns), meningitis (0.20 microns) and hepatitis A and E (0.027microns). Water-borne viral hepatitis E is common in Asia, northern and sub-Saharan Africa, and the eastern Mediterranean.

Chemical contamination is usually a by-product of civilization and includes inorganic contaminants (arsenic and other heavy metals) or organic toxins, fertilizers and pesticides. Nitrates in drinking water are from fertilisers and the oxidation of sewage effluents.

Chemical treatments

IODINE
Iodine is light sensitive and must be stored in a dark bottle. Tincture of iodine contains sodium iodide as well as iodine. Sodium iodide has no disinfectant activity but counts towards total iodine consumption. Iodine is not highly toxic, though prolonged use may cause health problems. People with thyroid problems, women over fifty, pregnant women and anyone allergic to shellfish should avoid iodine as a purification medium. Chlorine and silver disinfectant tablets are an alternative. The following measures should prove useful:

Percentage Iodine Clear Water Cloudy Water
1% Tincture 10 drops/gallon At least 20 drops/gallon
2% Tincture 5 drops/gallon At least 10 drops/gallon
4% to 6% Tincture 2 drops/gallon At least 4 drops/gallon
7% to 10% Tincture 1 drops/gallon At least 2 drops/gallon
Unknown Tincture 10 drops/gallon At least 20 drops/gallon

CHLORINE
Chlorine alone can easily be deactivated by organic matter and its action varies with pH, but it can be effective. If using liquid chlorine bleach from the local supermarket it should have at least 5.25% to 6% sodium hypochlorite (check the label) and contain no soap, fragrance or phosphates. Bleach loses efficiency with age and after a year it is at half strength. If the bleach is not dated then when you buy it note the date on the bottle. Add 20 drops of chlorine per gallon, mix thoroughly and let stand for an hour. A slight chlorine odour should be detectable. If not, repeat the dosage and let stand for at least another 15 minutes before using.Dry chlorine (calcium hypochlorite) from swimming pool supply stores is an alternative to liquid chlorine bleach. Providing it is kept dry, cool and in an airtight container it may be stored up to 10 years. Be aware that it is about ten times more powerful than liquid chlorine bleach (65% strength compared to 4-6%) and adjust the dosage accordingly.

STABILIZED OXYGEN
Stabilized Oxygen is an effective but lesser known treatment. Add 20 drops (1.3ml) to one gallon of water. Chlorine dioxide (a form of stabilized oxygen) products on the market include Aerox, Genesis 1000, Dynamo 2, Aerobic 07, and Aquagen.

More information

www.generalecology.com - First Need Products
www.katadyn.net – Katadyn products
www.msrcorp.com - MSR products
www.purwater.com - Pur Products
www.cascadedesigns.com - Sweetwater products
www.nsf.org - National Sanitation Foundation

NOTE: UPDATE

Iodine is no longer available in the EU - get the latest advice here.

Related articles here

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