 Water Cycle
The Earth’s supply of fresh water is a precious, and very limited, resource. Although 75 percent of the Earth’s surface is covered by water, less than 3 percent of that water is fresh, and only one half of 1 percent (0.5) is readily accessible for human use.
Water continuously moves from the atmosphere to the land to the oceans and back to the atmosphere in what is known as the hydrologic or water cycle. After precipitation falls (in the form of rain, snow or ice), it may immediately begin to evaporate from the ground surface, plants and trees, or water bodies, back into the air. A small percentage will run off into streams and rivers, eventually making its way to the oceans. Most of the water soaks into the ground, where it either replenishes shallow aquifers that sustain streams and springs, or seeps into deeper aquifers that serve as large underground reservoirs of freshwater. Water may remain in deep aquifers for centuries or millennia, gradually moving toward and into the Delaware River and the sea, where it evaporates again into the atmosphere.
Despite the fact that water is constantly moving through the hydrologic cycle and being recycled, it is not necessarily being returned to its prior pristine state. Humans interfere with the basic processes of the water cycle in a number of ways. These interferences include depleting groundwater supplies, paving over the land surface, and releasing pollutants onto the land where they can seep into groundwater and run off into local streams. Once polluted or degraded, it is very difficult to restore water to the standards that must be met for use by humans and wildlife. Thus pollution prevention is the most efficient and effective way to protect our water quality.
Return to the main Water Quality page.
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