An investigation of spatial and temporal drinking water quality variation in green residential plumbing

Drinking water chemical quality can deteriorate after water enters building plumbing. This study aimed to better understand seasonal and spatial water quality differences in a highly monitored net-zero energy residential building. Water flow rate and temperature were monitored for one year at the service line and at every fixture throughout the crosslinked polyethylene plumbing. Discrete water sampling events (58) were conducted at the service line, 1st floor kitchen sink, 2nd floor bathroom sink, the water heater, and 2nd floor shower. More than 2.4 billion online monitoring records were collected for fixture flow and temperature. In-building water stagnation time varied seasonally and across fixtures. Significant spatial and temporal water chemical quality variations were found. Average seasonal variability was found for service line temperature (15-23 degrees C) for the total chlorine residual (0.4-0.9 mg/L-Cl-2), NH3 (<0.01-0.4 mg/L-N), NO3 (0.1-0.8 mg/L-N), and Cu (32-81 mu g/L) concentrations. For 10.3% of the discrete water sampling events, service line water did not contain a detectable total chlorine residual. Water pH consistently and significantly increased in the plumbing system from 7.5 to 9.4, and total trihalomethane (TTHM) levels increased up to 89%. The service line total organic carbon level (0.5-0.6 mg/L) was consistent, but much greater in-building variability was found for cold (0.4-61.0 mg/L) and hot water (0.5-4.7 mg/L). Models are needed to predict chemical water quality at the faucet using service line water quality results and plumbing design and operational information. Building water sensor technology innovations are also needed.