Hydroelectricity is electricity produced by hydropower. It is a renewable source of energy, produces no waste, and does not produce carbon dioxide (CO2) which contributes to greenhouse gases. Hydroelectricity now supplies about 715,000 MWe or 19% of world electricity (16% in 2003), accounting for over 63% of the total electricity from renewables in 2005.

Although large hydroelectric installations generate most of the world's hydroelectricity, small hydro schemes are particularly popular in China, which has over 50% of world small hydro capacity.[1]
Renewable energy sources worldwide in 2005 (2004 for items marked * or **). Off-grid electric and ground source heat pumps not included. Source: REN21
Renewable energy sources worldwide in 2005 (2004 for items marked * or **). Off-grid electric and ground source heat pumps not included. Source: REN21

Some jurisdictions do not consider large hydro projects to be a sustainable energy source due to human and environmental impacts.