ABSTRACT
In most parts of the world, the days are long gone when rivers, lakes, springs, and wells from which one can directly drink, could readily meet almost all needs for high quality water. Where such water remains — mostly in high mountain regions untouched by mining, grazing, or industrial fallout — it must be protected by strict regulations. In the U.S., many states seek to preserve high quality waters with antidegradation policies. But most of the water that is used for drinking water supplies, irrigation, and industry, not to mention supplying a supporting habitat for natural flora and fauna, is much-reused water that often needs treatment to become acceptable.
