Water quality can vary dramatically from point to point in drinking water distribution systems. As water moves toward the periphery of a system the chlorine residual tends to disappear. This is usually due to the interaction of the disinfectant with the natural organic matter in the distributed water. Most drinking water systems utilize storage tanks to equalize system demand and to supply sources and to insure adequate fire flow and hydraulic reliability. Long residence times result from using storage tanks in a system which when coupled with chlorine demands in the distributed water result in the loss of disinfectant residuals. Careful consideration of tank location and system operating policies can result in improved water quality.