Some seeps to underground reservoirs. Almost all of this water eventually enters the cycle once more. People can alter the water cycle but little, so their primary supply of water is firmly fixed. But we can manage and conserve water as it becomes available when it falls on the land. If we fail to do so we lose the values that water has when used wisely.
Water management begins with soil management.
Because our water supply comes to us as precipitation falling on the land, the fate of each drop of rain, each snowflake, each hailstone depends largely on where it falls on the kind of soil and its cover. This action, soil erosion by water, repeated many times ruins land for most uses. Erosion, furthermore, is the source of sediment that fills streams, pollutes water, kills aquatic life, and shortens the useful life of dams and reservoirs. Falling rain erodes any raw earth surface. Bare, plowed farmland, cleared areas going into housing developments, and highway fills and banks are especially vulnerable.