https://phys.org/news/2018-07-flushing-lines-inconsistently-exposure.html

The research team surveyed homeowners and tested water samples from 376 New Orleans homes on the East Bank of the Mississippi River (the city's water source) between February 2015 and November 2016. Recruited homes met criteria for the potential presence of lead. Virginia Tech colleagues analyzed the water samples, which were first cold water draws, first hot water draws, draws after letting the water run for 30—45 seconds, 2.5—3 minutes or 5.5—6 minutes.

Overall, New Orleans water lead levels were typically low compared to the EPA's action level of 15 ppb. The analysis revealed a water lead level of 5 ppb in 88% of all samples from normal-use residential sites. More than half of all samples from normal use sites (60%) had detectable water lead levels of at least 1 ppb or higher. Water lead levels ranged from non-detectable (less than 1 ppb) to 58 ppb found in samples after flushing for 30-45 seconds. There was no significant difference in water lead level distribution after flushing for the various amounts of time until the six-minute mark after which the water lead level distribution decreased.