The design of the UPW distribution system directly impacts the capacity required in the polish plant, as well as the performance and reliability of steady pressure control. Implementation of end-of-return pressure control is a well demonstrated tool for capacity and reliability management, but its benefits and limits must be quantified. Where previous fabs may have had just one end-of-supply or end-of-main pressure control valve, new fabs often have two or more. Multiple zones or submains require methodical management of risk where many control valves are in play.