Along with soil water is another important factor essential for all life and production of food. The main source of water is precipitation. In India precipitation is not property distributed throughout the year. It is received within a few months of rainy season and that too in a critic manner. It may rain 50 to 125 mm. in one day causing flood and damage to crops and then there may be a dry spell for some days when crops may begin to will. Hence proper conservation of water as well as collecting surplus water in tanks and reservoirs of letting it out into the rivers assume great importance. To understand water conservation it is necessary to study the hydrologic cycle.
Water moves in a continuous cycle from ocean to clouds to earth and back to ocean. The water in the ocean is converted into vapour by the heat of the sun and this vapour moves in the form of clouds over the land and condenses into rain. Some rainwater enters the soil while the rest flows into streams and rivers and is either stored in tanks and reservoirs or allowed to go back to sea. Of the water that enters the soil some is stored for use by the plant some gets evaporated from the surface of the soil and some moves down to replenish the water table. This becomes the source of water for wells and springs. This cyclic movement of water is known as the hydrologic cycle. The water that is held by the soil in available form is essential for plant growth. It is not yet possible for the man to control rainfall but its infiltration and run off can be regulated to a great extent by improved management practices. Efforts should be made to store rain water either in the soil or in the reservoirs when it is in plenty and carry over to periods when rain water is not available. The former is known as conservation of water in soil, while the latter, conservation in reservoirs.