Potable water is water fit for human consumption and domestic use that is sanitary and normally free of minerals, organic substances, and toxic agents in excess of reasonable amounts of domestic usage in the area served and normally adequate in quantity and quality for the minimum health requirements of the persons served. Disinfect to inactivate virtually all recognized pathogenic microorganisms but not necessarily all microbial life (cf. pasteurize or sterilize). Turbidity the cloudiness caused by the presence of suspended solids in water, limiting the depth to which light can penetrate. Hydrologic cycle (water cycle) the process of precipitation, evaporation, and runoff through which water circulates through the earth. Water use use whereby very little water is lost to the atmosphere by evapotranspiration and practically the entire amount is returned to stream or ground. Water consumption the use of water resulting in a large proportion of loss to the atmosphere by evapotranspiration, includes use for drinking and irrigation. Surface water the water on the earth's surface as distinguished from subsurface water (groundwater). Pollution contaminants at a concentration high enough to endanger the aquatic environment. Hydrology the study of the properties of water, its distribution, and its behavior.