This study examines the impact of water purification on long-run old-age mortality. We
examine the effects of in-utero and early-life exposure to improvements in water quality due to city-wide water filtration programs in 25 major American cities on later-life old-age longevity. We employ data from Social Security Administration death records linked with the 1940 census. The difference-in-difference regressions suggest an improvement in longevity of about 3.4 months. A series of balancing tests do not reveal evidence that changes in sociodemographic and socioeconomic characteristics of individuals confound the estimates. Event-study results rule out concerns over preexisting trends in longevity. We also implement a full battery of sensitivity analyses and show that the effect is robust across specifications, subsamples, and functional form checks. Analyses using 1950-1970 censuses suggest that a portion of the long-term links can be explained by improvements in individuals’ education and income as a result of early-life exposure to water filtration. We also show that treated cohorts reveal improvements in height-for-age during early
adulthood.