The Power of Water begins at Niagara Falls, examining their unique role in the development of hydroelectric power. An illustrated explanation of water turbines stresses their versatility delivering dispatchable carbon-free energy at high ramp rates. The power of the largest hydroelectric plants worldwide and in the USA are compared. Dams’ large capital outlays, long lives, and multiple uses are examined, along with their susceptibility to multiyear droughts. Harnessing tidal power with barrages is then examined. Prospects for widespread geothermal power end the chapter.