Hydroelectricity does not "use" water, all of the water is returned to its source of origin. Hydroelectric power can be created 24/7 indefinitely assuming that the body of water it is utilizing never runs dry. It is also another absolutely clean source of energy. The power plants, once in place, do not create any waste byproducts in their conversion. Dams constructed can also shut their gates and conserve the water for use when power is in higher demand.