Describes a controlled evaluation of the effect of ultraviolet (UV) irradiation of hot and cold water supplies in a hospital colonised with Legionella, by inserting the UV units near the point of use. Describes four different experimental arrangements and supplies and discusses the results. Concludes the experiments demonstrate that UV plus prefiltration can prevent Legionella recolonisation after disinfection if the UV units are installed near the point of use. The advantages of UV include easy installation, low expense and no adverse effects on water or plumbing.

KEYWORDS: Hospitals, experiment, USA, ultraviolet radiation, drinking water, showers, legionnaires disease, bacteria, prefilters, ultraviolet lamps, water treatment