Over time, the reservoirs fill in with sediment deposited by the water. Some reservoirs in Africa may fill in less than 50 years, although most B.C. reservoirs will last over 200 years. The sites can be used only once and are not renewable. So hydroelectric energy is not a completely renewable resource. Water is a renewable resource.
Hydroelectric generators are clean and non-polluting to operate.
The water is not destroyed, consumed or polluted by generating electricity. Flowing water is free and reliable. Seasonal changes in water supply are fairly predictable. The water stored in the reservoir provides a continuous supply, even during dry weather. Once a dam is built, it costs very little to operate.