Chemical water quality impacts of extreme plumbing stagnation

Water quality has been known to degrade in building plumbing that has been stagnant for short periods of time (hours to weeks). However, there is a lack of publicly available knowledge about the impact of extreme stagnation periods on water quality. Residential plumbing can sometimes remain stagnant for months or years at a time due to long house selling times, seasonal traveling, or building closures/vacancies like that which occurred during the Coronavirus disease of 2019 (COVID-19) pandemic. To explore these phenomena, the present study involved controlled, pilot scale plumbing setups that were stagnated for months to years. The four identical plumbing configurations contained a water softener, a water heater, and copper and polyvinyl chloride (PVC) piping, all at room temperature conditions. No noticeable water chemistry changes were detected in stagnant piping, while some changes were detected in the softeners and heater tanks. It was found that total organic carbon (TOC) in water softener effluent correlated with stagnation time. In a 3-year stagnant softener, TOC levels reached 34.7 ppm as non-purgeable organic carbon (NPOC) in comparison to the 0.16 to 1.02 ppm as NPOC in the influent water. Chromium levels in softeners were also greater after stagnation time, though not linearly related to stagnation time. The tanks experienced different water chemistry changes than the softeners. Lithium in heater tanks correlated with stagnation time. In a 1.5-year stagnant heater tank, lithium levels reached 182 ppb, which is much greater than the non-enforceable federal health risk level of 10 ppb and the lithium levels of 7.8 to 10.9 ppb measured in the influent water. Sulfur and pH levels in tanks increased non-linearly with stagnation time. Sulfur compound speciation also became more diverse in stagnant tanks, with unknown sulfur compounds making up most of the sulfur measured. The stagnant water tanks were flushed with fresh tap water and sampled every five minutes of flushing to create washout curves that represent water quality parameters over flushing time. Lithium and sulfur both tended to decrease during flushing, with lithium levels sometimes decreasing below influent concentrations. Bench-scale analysis of tank sediment and anode rods revealed that sediment did not significantly contribute to contaminant levels in tank effluent during the author’s sampling activities and flushing. When placed in glass containers with tap water, pieces of the old anode rods increased aqueous sulfur levels indicating that sulfur was releasing from the anode rod’s biofilm or surface itself. Chemical analysis of shavings from the old anode rods revealed much greater levels of sulfur loading than sulfur in the new anode rod shavings. Study results suggest that softeners and tanks can introduce chemical water quality changes to water in stagnant plumbing and should be cleaned or replaced when plumbing is recommissioned. Additional recommendations are also provided.