This paper presents the results from an American Waterworks Association Research Foundation (AwwaRF) project that evaluated power quality (PQ) and its effect on ultraviolet (UV) disinfection. The main objective of this research was to determine the prevalence of PQ problems that may contribute to off-specification by gathering existing data previously compiled by the power industry and assessing PQ at several water treatment plants (WTPs). In addition, the range of power conditioning equipment was investigated to determine the appropriate power conditioning equipment based on the severity of the PQ problem. The specific objectives of the power quality research were as follows: compile PQ data available from power utilities and the Electric Power Research Institute (EPRI); monitor PQ and determine the range of PQ problems observed at a wide range of WTPs; determine the type and cost of power conditioning equipment that is available to address PQ problems; and, determine the PQ problems that trigger the need for different levels of power conditioning equipment. PQ monitoring at water utilities was completed as part of this research for short-term and long-term durations. The purpose of the short-term monitoring was to determine if there were any PQ problems due to WTP equipment interference (e.g., engaging a motor); the short-term duration monitoring will obviously not assess the long-term PQ events. The purpose of the long-term PQ monitoring was to determine if there were PQ problems from the power grid or within the WTP, and the long-term monitoring was completed over a minimum of five months. Includes 10 references, tables, figures.