Groundwaters can contain a variety of dissolved ions that can lead to major foulingproblems in ultraviolet (UV) disinfection systems. High iron and hardness can rapidly cause extensive fouling on the quartz sleeves protecting medium pressure lamps, and fouling reduces light transmission and limits disinfection ability. A Trojan UV8002(TM) medium pressure UV system was installed on a raw groundwater line at the Indianapolis Water Company (IWC) of Indianapolis, Indiana, to evaluate UV performance for this application. This IWC groundwater supplyhad iron levels as high as 1.8 mg/L and hardness values up to 500 mg/L as CaCO3. A physical-chemical wiper system using a proprietary food-grade cleaning solution was developed and implemented. Includes table, figures.