Man and most animals need a constant supply of water to live. Farmers need water for their crops. Hydroelectric dams hold back needed water and provide water for homes and industries. Trees, grasses, and other plant life play an important part in the natural circulation of water, and thus help conserve it. Without plants most water would run off as soon as it falls, taking away valuable soil. Rapid runoff would cause frequently floods, and leave little water during dry seasons. Nature has many ways of conserving and controlling water. But man often upsets the water balance in his desire to grow more crops. He drains ponds, swamps, and wet lands. He ploughs under natural sods, cuts timber, and dredges and straightens streams. These changes reduce natural storage of water and speed runoff. Water can be held on the land by planting vegetation. Forests and grass should be planted where there are no natural growths. Dams built across rivers help hold back the water. Reservoirs behind the dams store water during wet seasons for use in dry seasons. Dams help prevent floods by controlling the flow of water. Many towns and cities get their water from nearby lakes and rivers. Some communities dump sewage and garbage into the water, making it unfit to drink. Water pollution is one of our most serious problems. Progressive cities have sewage treatment plants. These plants return only safe water to the streams or lakes. Many states have laws that prohibit companies from dumping raw industrial wastes, such as liquids from a metal – planting factory, into streams. These wastes often endanger the supply of drinking water. They also kill fish. Most industrial wastes can be treated to make them harmless.
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