Chlorinated drinking water

Chlorine was already being poured into city water before 1919, but nobody could say how much was enough: the bleaching powder varied in strength, and the dose was guesswork. Abel Wolman, a Jewish engineer at the Maryland health department, worked out with the chemist Linn Enslow how to measure a water's chlorine demand and calculate the dose exactly. That calculation turned disinfection from an art into a standard, and typhoid and cholera vanished from the piped water of the industrial world. It is one of the least visible and most consequential public-health measures ever taken.

Part of “The Gifts of the Jews” — verified Jewish contributions to the world, with sources.