Hydropower or water power is power derived from the energy of falling water, which may be harnessed for useful purposes. Since ancient times, hydropower has been used for irrigation and the operation of various mechanical devices, such as watermills, sawmills, textile mills, dock cranes, and domestic lifts since ancient times. It is one of several renewable power sources. According to the Earth Policy Initiative, world hydroelectric power generation has risen steadily by an average 3 percent annually over the past four decades. In 2011, at 3,500 billion kilowatt-hours, hydroelectricity accounted for roughly 16 percent of global electricity generation, almost all produced by the world’s 45,000-plus large dams. Today hydropower is generated in over 160 countries.

Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally replenished). About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from hydroelectricity.

A lot of the increase in hydropower is due to China. China’s installed hydro capacity in the first half of 2009 was 172GW and constituted about 24% of total power generation capacity. In 2008, hydropower generated 563TWh, which was equivalent to 16% of China’s total and 85% of primary electricity generation. As China’s potential hydropower capacity (estimates range up to 600GW, but currently the technically exploitable and economically feasible capacity is around 400GW) is only about 25-30% utilized, there remains much space for further hyro development. In comparison, hydro utilization in the U.S. currently is 80% and in Norway, Iceland, and other countries it is at over 90%.

Four countries dominate the current hydropower production: China, Brazil, Canada, and the United States. Together they produce more than half of the world’s hydroelectricity.

Hydroelectric power in the United States is currently the largest producer of renewable power in the U.S. It produced around 67% of the total renewable power in the U.S. in 2008. In 2008 hydroelectric produced 6.4 % of the nation’s total electricity.

Brazil, the second-largest producer of hydropower worldwide, gets 86 percent of its electricity from water resources. It is home to an estimated 450 dams, including the Itaipu Dam, which generates more electricity than any other hydropower facility in the world—over 92 billion kilowatt-hours per year.

Hydropower is a mature energy in North America and Europe in that most of the potential sites have been developed. China has a lot more potential to develop as do others.