Sentinel lead pipe racks quantify orthophosphate’s dose-response in drinking water

Orthophosphate is used to minimize lead contamination of tap water, but its benefits are difficult to quantify since lead concentrations are plumbing-dependent. Homes serviced by lead pipe are ideal for monitoring orthophosphate treatment, but best practices dictate the removal of lead once identified, which complicates sampling plans. Here we explore an alternative: recovered lead pipe racks supplied with distributed drinking water at various locations within a water system. We also propose a strategy for analyzing the data based on the generalized additive model, which approximates time series as a sum of smooth functions. In this study, geometric mean lead release from pipe racks exhibited a pronounced dose-response, falling by 54% after an increase from 1 to 2 mg PO4 L-1, and then climbing by 55% after a decrease to 1.5 mg PO4 L-1. Data from nine sentinel homes were consistent with those from pipe racks: geometric mean lead at the high orthophosphate dose was 60% of that at the low dose. Our results demonstrate sentinel pipe racks as a viable alternative to at-the-tap sampling for non-regulatory corrosion control monitoring. They also provide a Bayesian framework for quantifying orthophosphate’s effect on lead release that can incorporate information from multiple sources.