Incidence of EBL (blood lead > or =10 microg/dL) for children aged < or = 1.3 years in Washington, DC increased more than 4 times comparing 2001-2003 when lead in water was high versus 2000 when lead in water was low. The incidence of EBL was highly correlated (R2 = 0.81) to 90th percentile lead in water lead levels (WLLs) from 2000 to 2007 for children aged < or = 1.3 years. The risk of exposure to high water lead levels varied markedly in different neighborhoods of the city. For children aged < or =30 months there were not strong correlations between WLLs and EBL, when analyzed for the city as a whole. However, the incidence of EBL increased 2.4 times in high-risk neighborhoods, increased 1.12 times in moderate-risk neighborhoods, and decreased in low-risk neighborhoods comparing 2003 to 2000. The incidence of EBL for children aged < or =30 months also deviated from national trends in a manner that was highly correlated with 90th percentile lead in water levels from 2000 to 2007 (R2 = 0.83) in the high-risk neighborhoods. These effects are consistent with predictions based on biokinetic models and prior research.

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The occurrence of particulate lead in drinking water deserves increased scrutiny. This is especially true because models of human exposure to lead, sampling protocols, analytical methods, and environmental assessments are often based on the presumed dominance of soluble lead in drinking water. Recent cases of childhood lead poisoning were tied to solder particles that detached from the plumbing and contaminated the potable water supply. In cases such as these, common samplehandling procedures can “miss” particulate lead present in water samples. In some instances, the actual amount of lead present in drinking water samples may be five times higher than that obtained using approved protocols. The presence of chloride, warmer temperature, and lower pH in the human stomach may render a significant fraction of this “missed” particulate lead as bioavailable when ingested.

Experimental tests and utilities' practical experience highlighted the importance of chloride‐to‐sulfate mass ratio (CSMR) in the control of lead leaching to potable water. The effect of higher CSMR was demonstrated in bench‐scale experiments using brass coupons and lead solder‐copper pipe joints, with the amount of lead leaching to water increasing by factors of 1.2–2.7 and 2.3–40.0, respectively. Anion exchange treatment, a switch in coagulant type, and other seemingly innocuous treatment steps can result in significant changes in CSMR. Practical data collected at three US utilities confirmed that alterations in CSMR can trigger serious lead contamination incidents.

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