Swamp coolers

(evaporative coolers)

  Air-conditioning equipment that removes heat by evaporating water. Evaporative cooling techniques are most commonly found in warm, dry climates such as in the Southwest, although they are found throughout the country. They usually work by spraying cool water into the air ducts, cooling the air as the spray evaporates.

  U.S. Dept. of Energy, Energy Information Administration's Energy Glossary