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Clean water is one of the most valuable and under appreciated resource of our planet. Approximately 70 percent of the earth's surface is covered with water, but only a small fraction of this water is fresh water that is actually available for consumption and productive use. Because of the unique properties of water, a dynamic cycle, known as the Hydrological Cycle, has developed on this planet. This cycle provides for the continuous movement, transformation, and remediation of water as it most through a series of solid, liquid, and vapor phases. One of the most confusing parts of this cycle is when the water becomes classified as groundwater. This is because it is not easy to visualize the actual flow and transformations (chemical and biological) that is going on as the water moves through the soil and rock.
The primary sources of water is Pennsylvania include: rainwater, stream inflow from other states, surface water (stored in lakes, streams, and ponds), and groundwater. In 1966, it was estimated that Pennsylvanians use approximately 6.6 billion gallons of water per day.
Because of the rural nature of Pennsylvania, groundwater provides approximately 85 percent of the water used for human consumption, but because it is difficult to set how water moves through the soil, unconsolidated material (sand and gravel) and bedrock. For some homeowners, they believe that the groundwater comes from a vast underground lake or from underground streams that come from Canada, Vermont, or even Maine. Even through there is a large database of information on groundwater in Pennsylvania, it still is difficult to really document the total available resource and actual movement and quantity without implementing a very elaborate system of monitoring wells, observation points, and background water quality data.
hydrologic cycle describes the constant movement of water above, on, and below
the earth's surface. As part of this cycle, water is transformed between
liquid, solid and gases states. Condensation, evaporation and freezing of
water occur in the cycle in response to the earth's climatic conditions.
Figure 1 presents components of the hydrologic cycle that directly affect
Figure 1. Components of the
The hydrologic cycle begins with water evaporation from the earth's soil, plant and water surfaces to form water vapor. The energy required to evaporate water is supplied by the sun. The vast majority of evaporation occurs from the oceans. It is estimated that 39 inches of water annually evaporate from each acre of ocean (Water of the World, US Geological Survey). Water vapor is drawn into the atmosphere by temperature gradients and can be transported over hundreds of miles by large air masses. When water vapor cools, it condenses to form clouds. As water condenses within clouds, water droplets increase in size until they fall to the earth's surface as precipitation such as rainfall, hail, sleet or snow.
Approximately 50 to 90 percent of the water that falls to the earth's surface enters the soil. This water can become groundwater but most of it evaporates from the soil surface, used by vegetation via evapotranspriation, or flows to streams and springs as interflow. Water that passes through the root zone may continue to move downward to reach the groundwater. In soils with fragipans, clay pans or other low permeable strata of a limited extent, this water may create a seasonal high or perched water table. The distance water has to travel to reach groundwater can range from a few feet to hundreds of feet. Water movement toward groundwater may take hours or years, depending on the depth to the aquifer and the characteristics of the unsaturated zone.
Once in the groundwater, water will slowly move to discharge points which may include: springs, streams, lakes, wetlands, or even the ocean. Groundwater moves slowly within the groundwater aquifer, often remaining in storage for 100s of years.
For Pennsylvania, the annual precipitation ranges from 30 to 60 inches per year with a mean rainfall of approximately 41 inches. Approximately 55 to 60 percent of the precipitation occurs during the warmer months. Of this approximately, 20 inches is returned to the atmosphere via evapotranspiration or evaporation, 12 to 15 inches infiltrates into the groundwater system, and direct runoff accounts for approximately 6 to 12 inches of water. Groundwater storage in Pennsylvania is equivalent to approximately 60 inches of water or a conservative estimate of over 47 trillion gallons, of which, 9 to 12 trillion is naturally discharged to springs, seeps, streams, and lakes.
During periods of drought water supplies become very low. Water-use restrictions are set for communities in order to preserve water. In this situation water can only be used for drinking and sanitation purposes and not for tasks that include washing cars and watering lawns. Here are 19 ways to help conserve water:
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