Role of water service lines in the propagation of user-induced transients: Laboratory investigation on a highly instrumented, full-scale replica

Water service lines (SLs) are the hydraulic interface between the water distribution network and household plumbing systems (PSs). However, their vulnerability to rapid pressure transients caused by everyday household water use is still poorly understood due to the scarcity of detailed experimental investigation. Therefore, a highly instrumented full-scale laboratory replica of a complete “minor system”, consisting of a SL and a PS, was developed to: (i) comprehensively measure user-induced transients under fully controlled conditions, and (ii) investigate how SL characteristics govern those transients. The facility incorporates interchangeable SLs of various diameters and materials commonly used in practice, as well as a branched PS made up of pipes representative of modern residential installations. During a series of tests, flowrate and high-frequency pressure data were collected at several locations of the facility to accurately characterize the complex pressure wave dynamics. Step changes in demand were produced by a custom-built manoeuvring apparatus featuring fast-acting solenoid valves installed at four typical domestic outlets, ensuring repeatable test conditions. The analysis of high-frequency data revealed that closures generated pressure variations of up to 200 m within the plumbing system and 50 m within the SL; however, only a few meters were transmitted to the main network. Peak and cumulative hoop stresses were greatest for metallic and small-diameter SLs, and lowest for oversized and plastic SLs that promoted wave attenuation. The terminal branches of the PS experienced the greatest pressure variations, indicating them to be critical sections. The findings of the study clarify the mechanisms that contribute to the high failure rate of minor elements and provide quantitative guidance in the selection of the appropriate diameter and material during replacement operations. They also emphasize the importance of transient mitigation strategies for both utilities and users.