American drinking water supplies are among the safest in the world. The disinfection of water has played a critical role in improving drinking water quality in the United States. In 1908, Jersey City, New Jersey was the first city in the United States to begin routine disinfection of community drinking water. Over the next decade, thousands of cities and towns across the United States followed suit in routinely disinfecting their drinking water, contributing to a dramatic decrease in disease across the country.

https://www.cdc.gov/healthywater/drinking/history.html