Man and most animals need a constant supply of water to live. Farmers water for their crops. Hydroelectric dams hold back needed water and provide power for homes and industries.

Trees and grass, and other plant life play an important part in the natural circulation of water, thus help conserve it. Without plants most water would run as soon as it falls, taking away valuable soil. Rapid runoff would cause frequent 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 land. He ploughs under the natural soil, 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 plating 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 season use in dry seasons. Dams help prevent floods by controlling the flow of water.

Note: to dredge = to make a river deeper