An important concern in a cross-sectional study such as ours is that the cities that installed lead pipes in the nineteenth century might have differed from the cities that did not in unobserved ways that were correlated with their homicide rates. Based on available data on the characteristics of the cities in our sample, we find little evidence that the cities that used lead pipes differed in observable ways from the cities that did not. Although larger cities, denser cities, and cities with comparatively low rates of home ownership were more likely to have used lead pipes, so were better-educated cities. High-homicide southern cities, meanwhile, were less likely to have used lead pipes. When we predict whether cities used lead pipes using all covariates, the only difference that remains statistically significant is the city population.