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For an estimated explanation of where Earth's water exists, look at this bar chart. You may know that the water cycle describes the movement of Earth's water, so realize that the chart and table below represent the presence of Earth’s water at a single point in time. Here is a bar chart showing where all water on, in, and above the Earth exists. The left-side bar chart shows how almost all of Earth's water is saline and is found in the oceans. The world's total water supply of about 332.5 million cubic miles of water, over 96 percent is saline and of the total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of fresh water is in the ground. Fresh surface-water sources, such as rivers and lakes, only constitute about 22,300 cubic miles (, which is about 1/150th of one percent of total water. Yet, rivers and lakes are the sources of most of the water people use every day. In the left bar, notice how only 2.5% of Earth's fresh water - the amount needed for life to survive. The center bar shows the breakdown of freshwater. Almost all of it is locked up in ice and in the ground. Design of water supply and sanitation scheme is based on the projected population of a particular city, estimated for the design period. Any underestimated value will make system inadequate for the purpose intended; similarly overestimated value will make it costly. Water demand includes water delivered to the system to meet the needs of consumers, water supply for firefighting and system flushing, and water required to properly operate the treatment facilities.
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