The Link between Transient Surges and Minimum Pressure Criterion in Water Distribution Systems

The minimum pressure criterion (MPC) is considered as the minimum standard for delivering water pressure when designing water distribution systems (WDSs). This criterion is established by political jurisdictions and is different around the world. A low value of the MPC may reduce water consumption (e.g., faucet, showers, and lawn watering) and also lead to efficient operation through reduced energy use, leakage, and frequency of pipe breaks. However, if this criterion is too low, the system may be more susceptible to low pressure failures, either hydraulic (e.g., an inability to supply the required flow) or safety related (e.g., increasing the risk of an intrusion event and pipe bursts associated with hydraulic transients). Thus, although it may not have been part of the original intent, there is a direct connection between MPC and transients that should not be ignored. This paper looks specifically at the role of MPC and how it affects the system response in transient conditions to raise the awareness about issues that can arise from changes in MPC. First, the definition of MPC and the possible effects of changes in the MPC on WDSs during transient events are briefly explained. Then, two case studies are developed to explore the role of MPC in transient pressures. The results show, not surprisingly, that using surge control strategies is more efficient than increasing the MPC to prevent unwanted surge pressures.