U.S. Department of Energy - Energy Efficiency and Renewable Energy

Tribal Energy Program

How Hydropower Works

Water constantly moves through a vast global cycle, evaporating from lakes and oceans, forming clouds, precipitating as rain or snow, then flowing back down to the ocean. The energy of this water cycle, which is driven by the sun, can be tapped to produce electricity or for mechanical tasks like grinding grain. Hydropower uses a fuel — water — that is not reduced or used up in the process. Because the water cycle is an endless, constantly recharging system, hydropower is considered a renewable form of energy.

A diagram of the water cycle showing how precipitation from clouds falls on land and then is returned to clouds to complete the cycle. Water moves from the earth to the clouds through evaporation. Some of the water evaporates from the ground surface and some flows into the ocean where it evaporates later. Some precipitation from clouds seeps into the earth to form groundwater, some of which does not evaporate, and therefore is not part of the water cycle.

The water (hydrologic) cycle.

When flowing water is captured and turned into electricity, it is called hydroelectric power or hydropower. There are several types of hydroelectric power facilities; they are all powered by the kinetic energy of flowing water as it moves downstream. Turbines and generators convert the energy into electricity, which is then fed into the electrical grid to be used in homes and businesses and by industry.