Hydrosphere

The hydrosphere includes all the waters of the oceans, lakes, and rivers, as well as groundwater—which exists within the lithosphere. Approximately forty million cubic miles of water cover or reside within the Earth. The oceans contain about 97 percent of all water on Earth. The other 3 percent is freshwater: (1) snow and ice on the surface of Earth contains about 2.25 percent of the water; (2) usable groundwater is approximately 0.3 percent; and (3) surface freshwater is less than 0.5 percent.

In the United States, for example, average rainfall is approximately 2.6 feet (a volume of 5,900 cubic kilometers). Of this amount, approximately 71 percent evaporates (about 4,200 cubic centimeters), and 29 percent goes to streamflow (about 1,700 cubic kilometers).

Beneficial freshwater uses include manufacturing, food production, domestic and public needs, recreation, hydroelectric power production, and flood control. Streamflow withdrawn annually is about 7.5 percent (440 cubic kilometers). Irrigation and industry use almost half of this amount (3.4 percent or 200 cubic kilometers per year). Municipalities use only about 0.6 percent (35 cubic kilometers per year) of this amount.

Historically, in the United States, water usage is increasing (as might be expected). For example, in 1975, 40 billion gallons of freshwater were used. In 1990, the total increased to 455 billion gallons. Projected use in 2002 is about 725 billion gallons. The primary sources of freshwater include the following:

1. captured and stored rainfall in cisterns and water jars;

2. groundwater from springs, artesian wells, and drilled or dug wells;

3. surface water from lakes, rivers, and streams;

4. desalinized seawater or brackish groundwater; and

5. reclaimed wastewater.