Boston’s secret ingredient? Watershed protection. Between 1985 and 2012, the Massachusetts Water Resources Authority—from which Boston buys its water—purchased conservation land in the watersheds that feed the Quabbin and Wachusett reservoirs to the city’s west, the sources of Boston’s water.
Forests in the protected area clean the water naturally so that by the time it gets to the city it requires only limited filtering. There’s no need for the cocktail of chemicals most cities’ water utilities use.