An evaporative cooler is disclosed comprising an amount of water, an anti microbial catalyst, and a source of ultraviolet radiation. A preferred anti-microbial catalyst material is titanium dioxide. The ultraviolet source may by natural sunlight, or it may be driven by electricity. In a preferred embodiment the ultraviolet source is an electric one, powered by a solar panel. A preferred evaporative cooler is a dew-point cooler.