While water covers approximately 71 percent of Earth's surface, only three percent is suitable for human consumption. People can not access most of this water, because it is frozen in polar ice caps or beneath the planet's surface. Available sources for water are derived largely from developments including the recycling and conservation of available water resources, and techniques, such as filtration, which make water potable.
Oceans cover most of the Earth, and contain about 97 percent of the water on the planet. This water has a high salt content and is unfit for human use. With the depletion of scarce freshwater sources, methods for removing salt from ocean water, including desalination or distillation, have not been cost-effective. Although untreated sea water is not suitable for human consumption, oceans remain a valuable resource, because they provide food, recreation, oil and a transportation route for trade.
Rivers and Streams
Rivers and streams cover the globe and run through every nation, providing drinking water and recreational areas for swimming, boating and fishing. Rainfall and melting snow continually replenish these waterways. However, weather patterns impact water depth. Severe droughts dry rivers up, while too much rainfall can cause flooding when the water overflows a river's banks. Because rivers and streams cross national boundaries, water rights remain a topic of political debate and conflict.
Lakes are natural or man-made depressions on the surface of land that hold water. Natural lakes occur due to geological processes, such as weathering and erosion. Man-made lakes, also called reservoirs, occur when people dam up rivers and streams or divert the flow of these waterways in order to contain a large amount of water in one area. Lakes provide an energy source for generating electricity, offer recreational areas for swimming and fishing and provide a source of drinking water for many communities. Rainfall replenishes lake water; however, this water is vulnerable to pollution.
Water seeps into the ground from surface run-off and precipitation. As the water enters the ground, part of it clings to plant roots and particles of soil and becomes trapped, creating a water table. Aquifers beneath the water table collect the seeping water, which is called groundwater. According to the United States Geological Survey, or USGS, approximately 50 percent of Americans use ground water for drinking and other household uses. People collect this water by drilling or digging wells that pump the water from below the water table to the surface.