This is from:

http://www.union.rpi.edu/railroad/Time-line.html#1900

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1913

First chlorination of municipal water supply. According to American Chemical Industry, the Electro Bleaching Gas Co. was founded in Niagara Falls, NY around 1910, liquefying chlorine with electricity and using it directly as a bleach. At that time, this popular honeymoon destination had an appalling typhoid fever epidemic, and the growing tourist traffic caused the spread to other parts of the country.

In 1913, the company tried a revolutionary experiment, using their liquid chlorine to sterilize the public water supply of Niagara Falls. Despite the crude equipment used at first, typhoid fever rates dropped dramatically, and other cities soon followed with chlorinating their water supply.

Prior to this, the only drinking water that was safe was from springs, and rather than drinking fresh water, people got their water from tea and coffee (boiling it in the process) or from alcoholic beverages, where the alcohol in a sense sterilized the water. Even the carbonation and sugar used for sodas would help kill off some of the bacteria.

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