Whether by heating, chemical or filtration treatment, no one method will render water absolutely safe and pure to consume. If you find yourself in a situation where water available to drink is suspect, here are three main ways to make it safer.

1. HEATING

Considered effective for biological contaminants, bringing a container of water to a round boil for at least one minute or heating to near boil and covering for five minutes will disinfect it. Boiling (to 185 degrees) will work even at higher elevations, but if snow or ice are used, make sure all of it has melted before beginning disinfecting time. After boiling, water will taste flat because the dissolved oxygen is gone. Pouring it between clean containers or shaking a partially full container will make it more palatable. Heating, however, will not remove or neutralize many chemical or metallic contaminants. Those must be dealt with by filtration or chemical processes.

2. CHEMICAL

As with heating, primary chemical treatments should be done to kill off any harmful biologicals. Iodine or chlorine are the most common disinfectants used in water purification. But their effectiveness is controlled by suspended solids (silt or vegetable matter) clouding water and how cold it is. Some micro-organisms are resistant to mild levels of chemicals, too. Before adding a disinfectant, repeatedly strain the water through a fine cloth or activated charcoal. If it is from a cold source, also let it warm up. The amount of disinfectant can vary according to contact time, but usually 10 drops per quart for one-half hour is recommended.

3. FILTRATION

The extent to which water can be clarified and disinfected via filtration usually depends on the material through which the water is passed. Depending on their size, some organisms and inert suspended particles will not be captured in improperly selected filters. Filters also can be designed to remove some dissolved compounds or metallic substances. Most often, activated charcoal is the first choice for this, but some filters are specifically designed to chemically react with contaminants. Check filter devices carefully to determine what size or type of contaminants they remove.

MORE CRYSTAL CLEAR TIPS

-- To make the final treatment as effective as possible, always use the clearest water you can find. Otherwise, pre-strain murky water to remove as much solid material as possible or let it stand overnight to allow them to settle out, then pour off the clearer water.

-- If you buy and use a commercial water treatment device for hiking and backpacking, handle it with care. Dropping or banging it on a hard surface can damage the filter medium, allowing untreated water to get through.

-- If iodine compounds are used, also be aware of possible allergic reactions in those who drink the treated water.

-- For more details about emergency treatment of water for drinking check out:

www.epa.gov,

www.outdoors.org, or

www.princeton.edu

Sources: U.S. Environmental Protection Agency, the Appalachian Mountain Club and Princeton University's Outdoor Action Program