Surface Water: Rivers and Lakes - Characteristics Of Rivers And Lakes, The Need For Pollution Control, Assessing Water Quality, Water Quality Of The Nation's Riversand Streams

At any one time, more than 97% of all the water in the hydrologic cycle is contained in the earth's oceans. By comparison, the rivers contain only 0.0001% of the earth's water at any one time and its lakes 0.007%. Nonetheless, this tiny fraction of the total water supply has shaped the course of human development. Throughout human history, societies have depended on these surface water resources for food, drinking water, transportation, commerce, power, and recreation.

In the United States, water from streams, rivers, and lakes accounts for 76% of the total freshwater consumption; the rest comes from groundwater. Of the total available supply—about 1,380 billion gallons per day (bgd)—only about 262 bgd is actually used daily. Public utilities depend on surface water for about 63% of their water needs; industries consume surface water for 80% of their requirements; and crop irrigation uses surface water for about 58% of its water needs.

The withdrawal of surface water varies greatly by location. In New England, for example, where rainfall is plentiful, less than 1% of the annual renewable water supply is used. By contrast, almost the entire annual supply is consumed in the area of the arid Colorado River Basin and the Rio Grande Valley.