Estimating Lead Concentrations in Drinking Water after Stagnation in Lead Service Lines Using Water Quality Data from across the United States

Water samples collected sequentially from a tap can have lead concentrations that vary as a result of differences in pipe materials in contact with water during stagnation. The revised Lead and Copper Rule will require a 5th liter sample instead of a 1st liter sample for monitoring lead at residences with lead service lines. However, there is limited information regarding the extent to which the 1st and 5th liter lead concentrations will differ. From a pool of published sequential sampling data, the 5th liter lead was higher than the 1st liter lead in 77% of the studies. A national database was created with 90th percentile 1st liter lead and water quality for 434 very large public water systems in the United States in 2019. A solubility-based model estimated the dissolved lead concentrations in equilibrium with lead corrosion products predicted to form in these systems. The predicted equilibrium lead concentrations exceeded the 90th percentile 1st liter lead in 98.9% of systems that reported both pH and alkalinity. For the pool of published sequential sampling data, the predicted equilibrium lead concentrations were closer to the measured 5th liter than 1st liter lead.