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Historically, Philadelphia sourced its water by the Fairmount Water Works, the nation's first major urban water supply system. In 1909, Water Works was decommissioned as the city transitioned to modern sand filtration methods. Today, the Philadelphia Water Department (PWD) provides drinking water, wastewater collection, and stormwater services for Philadelphia, as well as surrounding counties. PWD draws about 57 percent of its drinking water from the Delaware River and the balance from the Schuylkill River. The public wastewater system consists of three water pollution control plants, 21 pumping stations, and about 3,657 miles of sewers. A 2007 investigation by the Environmental Protection Agency found elevated levels of Iodine-131 in the city's potable water.[citation needed] In 2012, the EPA's readings discovered that the city had the highest readings of I-131 in the nation. The city campaigned against an Associated Press report that the high levels of I-131 were the results of local gas drilling in the Upper Delaware River.[citation needed]

How many miles of sewers are in the city?
3,657 miles