Although the U.S. Environmental Protection Agency (EPA) sets water-quality standards for municipal water supplies and oversees the enforcement of those standards, no water supplier can test for every possible contaminant. According to the University of Wisconsin Extension, an estimated 42 million Americans draw their drinking water from wells, springs, cisterns or streams. Although municipal building codes dictate installation requirements, such as minimum distance of a potable water source from a septic system, no government agency monitors the quality of water drawn from these sources.
Boiling
Boiling water kills virtually all disease-causing biological contaminants, including Giardia lamblia and Cryptosporidium, which cause a variety of intestinal disorders. The U.S. Environmental Protection Agency recommends first filtering water that appears cloudy or contains sediment and then bringing the water to a rolling boil for at least one minute and then allowing the water to cool before drinking. The filtration method may be as simple as pouring the water through a clean cloth.
Although boiling destroys microorganisms present in water, it does not remove most organic compounds, metals, chloride or nitrate.
Chemical Purification
Chemical purification is generally recommended in emergency situations, such as areas affected by floods or hurricanes. The method involves adding an oxidizing agent such as bleach or iodine to water and allowing it to sit for a period of 30 minutes. When performed correctly, chemical purification is highly effective against microorganisms, but the taste of the water is adversely affected. Rick Curtis, author of "The Backpacker's Field Manual," states that addition of vitamin C, including drink mixes that contain vitamin C, to the water removes any taste, color or odor. Vitamin C should only be added, however, after the iodine or bleach has been given sufficient time to sanitize the water.
According to the EPA, household bleach, which typically contains 4 to 6 percent hypochlorite, may be added to drinking water at a rate of 1/8 teaspoon or about eight drops per gallon. The water should then be shaken or swirled and allowed to stand, preferably covered, for about 30 minutes.
Tincture of iodine, sold as over-the-counter topical antiseptics for wounds, may be added to water at a rate of 20 drops per gallon. The water should not be consumed for at least 30 minutes.
Outdoor and camping stores also sell water purification tablets that may be either iodine- or hypochlorite-based. Follow the manufacturer's instructions when using such tablets.
Filtration
Filtration systems represent the most convenient and practical water purification method. Filtration systems fall into one of two categories: point-of-use (POU) or point-of-entry (POE), according to Michigan State University Cooperative Extension Service. POE systems represent whole-house water treatment solutions with substantial initial costs.
The simplest filtration systems consist of a pitcher equipped with a charcoal or activated carbon filter. Tap water is poured into the top of the pitcher and then flows through the filter media into the reservoir by force of gravity. Such systems are inexpensive-- $20 or less, 2010 prices. Filters that screw directly onto the faucet tap operate on the same filtration principle but flow somewhat faster because they operate under household water pressure. Charcoal filters remove organic contaminants such as pesticides andvolatile organic compounds, some metals and chloride, but are ineffective against biological contaminants. Such filters are also impractical for producing more than one or two gallons of purified water per day. High-flow filters that mount under a sink provide larger quantities of filtered water, but their installation is more complicated and initial costs are higher.
More elaborate and expensive POU systems include reverse osmosis systems, stills for producing distilled water and chemical oxidation systems that generate and inject ozone into the water. Reverse osmosis and distillation are effective against both biological contaminants and metals, but are limited in their effectiveness against organics. Chemical oxidation systems destroy microorganisms and some organics, but are ineffective against metals.
References
- University of Wisconsin Extension: Drinking Water and MTBE
- Princeton University: OA Guide to Water Purification
- U.S. Environmental Protection Agency: Emergency Disinfection of Drinking Water
- U.S. Environmental Protection Agency: Water Health Series -- Filtration Facts
- Michigan State University Cooperative Extension Service: A Guide to Home Water Treatment
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