It is best to prevent contamination of safe water supplies, and conserve them for high-quality uses. When all else fails, water is treated. Distillation, the process of heating water to produce water vapor, is a simple, low-tech way to eliminate pollution and purify water for drinking, cooking, and laboratory use. Distilled water is pure but has a flat taste.
The most important health-related water treatment is disinfection to destroy microorganisms. It is required for surface water, or for groundwater in contact with surface water. Primary water treatment begins with filtration, followed by disinfection to kill microorganisms in the water. Secondary treatment keeps the level of disinfectant high enough to prevent microorganism re-growth. Disinfection is accomplished by a variety of means, including chlorination, nanofiltration (filtration for extremely small organisms), ultraviolet (UV) light, bromine, iodine, ozone, and heat treatment.
Suspended particles and some materials affecting color or taste can be removed by filtration. Filters can also remove some bacteria, including Giardia cysts. The water is passed through permeable fabric or porous beds of filtering material.
Aeration, also called oxidation, improves taste and color and helps to remove iron and manganese. Water is sprayed or run down turbulent waterfalls to expose as much of its surface to air as possible. Sculptural waterfalls called flowforms, which have rhythmical, pulsating, or figure-8 patterns, are both efficient and beautiful. The retailer Real Goods in Hopland, California, uses flowforms as part of a recycled water irrigation system. Aeration improves the flat taste of distilled and cistern water, and removes odors from hydrogen sul-
fide and algae. Aeration may make the water more corrosive.
The addition of fluoride to public water supplies has greatly reduced the amount of childhood tooth decay. Once we develop our adult teeth, we no longer benefit from the fluoride, and too much fluoride can cause yellow mottling on the teeth.
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