Water Quality

The suitability of water for aquatic life and for human use depends on its quality. All natural waters contain dissolved inorganic and organic substances. The total dissolved solids burden of rivers is generally between 20 to 2,000 parts per million and may be higher in groundwater. In natural (unpolluted) surface waters, the major dissolved solids are calcium, magnesium, sodium, potassium, sulfate, chloride, carbonate, bicarbonate and silica. In the United States the average concentration of dissolved matter ranges from about 50 parts per million in the humid western mountains and the Appalachian up to 1,000 parts per million in the arid non-mountainous region of the West.

Many pollutants may also be found in solution, either as large increases of substances normally present, such as nitrates, phosphates and certain metals or as synthetic substances, such as pesticides. The PH of water, a measure of acidity of alkalinity, is an important quality increased (from normal pH of 5.6 to between pH 4 and 5) in some regions by atmospheric pollutants. Another measure of water quality is dissolved oxygen. Animals that live in water depend on dissolved oxygen for life. A marked decrease of dissolved oxygen because of bacterial decay of organic wastes has been a major impact of water pollutant.

Suspended sediment affect water quality by reducing light penetration, smothering fish eggs and other bottom life, filling lakes and reservoirs, and making water undesirable for many uses. Fecal coliform bacteria in water are an important index of water quality. Delivered from the intestines of mammals (including humans), they indicate the possibility that disease organisms are present. Water temperature, a final qualitative factor, influences the metabolic rate of aquatic organisms and the rates of chemical reactions. Significant increases of temperature caused by industrial discharges of heated water may be detrimental to aquatic life, a condition termed thermal pollution.