This paper explores the possibility that preventive measures, such as pulsed UV light photons (PUV) or ozone treatment may provide an effective means of microsporidia control in water supplies with the potential for improving drinking water safety, especially for immunocompromised patients. This study was performed to examine the in vitro growth potential of Encephalitozoon sp. after exposure to 0.5-1.0 mg/l ozone or 50-200 mws pulsed UV light (PUV). PUV wavelengths were produced by the Innovatech INC. system, specifically designed for inactivation of waterborne pathogens in small-volume water supplies. It was found that PUV exposure (50-200 mws) of Encephalitozoon spores in water inhibited the subsequent growth of spores in an RK-13 cell in vitro viability assay. These results indicate that 50 mws of PUV treatment may have a lethal effect on microsporidia spores in water and that PUV treatment has the potential to be an effective small-volume water treatment for microsporidia. Also, ozone at concentrations as high as 1.0mg/l was not able to completely diminsh growth of spores in an RK-13 cell in vitro viability assay.