Quiescent waters in potable water storage tanks are associated with water quality problems such as thermal stratification, biofilms, excessive disinfection byproducts and disinfectant residual loss. Ice formation in distribution-system reservoirs is another challenge faced by water utilities in northern climates during winters. Thick layers of ice often form at the surface in storage tanks during prolonged periods of subfreezing weather. Steel tanks can expand during ice formation, causing structural damage and water leakage. The vertical movement of huge ice chunks with inflows and outflows may further damage the tanks. This report discusses the causes of ice buildup in potable water reservoirs and describes applications of Medora Corporation active mixing technology to prevent excessive ice formation.