Historically, water utilities have managed distribution systems primarily to provide reliability of service such as adequate pressure and fire flow capabilities. However, increasingly stringent regulations such as the Stage 2 D/DBP Rule have added a focus on also maintaining acceptable water quality in the distribution system. Maintenance of distribution system water quality is now a major challenge for many utilities. Water quality challenges in the distribution system may include loss of disinfectant residual, increase in disinfection byproducts, biological growth, and for systems that use chloramines, nitrification. Storage tanks that are underutilized and have poor mixing characteristics represent a significant potential for water quality degradation within the distribution system. Computational fluid dynamic (CFD) modeling and water temperature measurements can be very effective tools to predict mixing characteristics inside the tanks. This paper focuses on the use of CFD modeling and temperature measurements to determine mixing characteristics in storage tanks, using a case study, the City of Virginia Beach. The results from mixing predictions are verified by water quality data and used to identify the storage tanks with inadequate mixing characteristics and thus the greatest potential for water quality degradation. Once the nature of the mixing problem is identified, it becomes easier to make the appropriate physical and operational modifications to improve mixing in the storage tanks. This paper also presents general recommendations for improving mixing, and reports on actual physical modifications that have improved mixing characteristics in a storage tank. Includes table, figures.