The need for reliable and effective means of treating drinking water to prevent illness due to consumption of microbe contaminated water has been realized as early as the 19th century. The development of ultraviolet light as a means of disinfecting water, which began as early as 1901, it's advantages and disadvantages are outlined in this paper. More importantly, system devices used in water treatment must have proper design, developed through awareness of flow dynamics, the impact on ultraviolet output imparted by water characteristics both organic and inorganic, and a knowledge of microbial inactivation requirements. Reliable and valid methods of performance evaluation are important to ensure standardized industry practices, thereby safeguarding the consumer. This paper discusses various standard test methods for evaluating performance of UV water treatment devices, with test results for such a device.