Acanthamoeba is a microscopic, free-living ameba that is relatively common in the environment. This ameba has been isolated from water (including natural and treated water in pools or hot tubs), soil, air (in association with cooling towers, heating, ventilation and air conditioner [HVAC] systems), sewage systems, and drinking water systems (shower heads, taps). By The Encyclopedia of Earth (EoE), an electronic reference about the Earth, its natural environments, and their interaction with society.