The quality of a public water supply although acceptable when it leaves the treatment plant, may deteriorate before it reaches the user. Deterioration may be caused by either chemical or biological transformations or by a loss of system integrity. There have been a growing number of coliform regrowth and biofilm formation situations reported in distribution systems. A water quality prediction model has been developed in cooperation with the North Penn Water Authority. The cooperative agreement has focused on the hydraulic behavior of the system, examination of historical water quality sampling data, and steady-state modeling of water quality within the distribution system.