Water- A clear, colorless, odorless, and tasteless liquid, H 2 O, essential for most plant and animal life and the most widely used of all solvents. Freezing point 0 °C (32 °F); boiling point 100 °C (212 °F); specific gravity (4 °C) 1.0000; weight per gallon (15 °C) 8.337 pounds (3.772 kilograms)

Fresh water- Water that contains very little salt, less than half of one percent in concentration. Streams, Rivers, Ponds, Lakes, and inland seas are freshwater if their water source is Precipitation. Most of Earth’s freshwater supply is stored as ice. The ice in Greenland and Antarctica holds between 70 and 90 percent of all the freshwater on Earth. One-fifth of the world’s liquid freshwater is in Lake Baikal in Russia. The Great Lakes in North America hold another fifth of the world’s supply of liquid freshwater

Human use of natural waters, particularly of freshwater resources, has increased steadily over the centuries. It is unlikely that this trend will change given the continued growth of population and the ever-widening utilization of water for agricultural, industrial, and recreational purposes. This situation has given rise to growing concern over the availability of adequate water supplies to accommodate the future needs of society. Surface-water resources are already being used to their maximum capacity in various regions of the world, as, for example, in the southwestern United States. Quantity of water is not the only concern. Overuse has resulted in the progressive deterioration of water quality. Seepage of mineral fertilizers (phosphates and nitrates), pesticides, and herbicides into surface and subsurface waters has not only rendered them unfit for human consumption but also disrupted aquatic ecosystems. Lakes and rivers also have been contaminated by the improper disposal of sewage, the discharge of untreated industrial wastes (including such toxicants as polychlorinated biphenyls, or PCBs), and the release of heated wastewater from nuclear-power plants and other industrial facilities, which results in thermal pollution and its attendant problems.

Most of California's fresh water comes from water reservoirs in the Sierra Nevadas and other places. In the San Francisco Bay Area, 85 percent of the fresh water comes from the Yosemite Valley. There, snow melts and eventually collects in the Hetch Hetchy reservoirs. Amazingly, this water is pure enough so that it does not need to be put through a filtration system. Once collected, water from the Hetch Hetchy reservoir flows to San Francisco through a pipeline system driven by gravity.

Hetch Hetchy Reservoir Information

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