Most large urban areas in New York State are served by municipal sewer systems, many of which commingle stormwater with the wastewater from homes and businesses in combined sewer systems. The flows from combined sewers can overwhelm treatment systems and have a harmful impact on the environment. This report, as part of the Office of the State Comptroller’s infrastructure series, describes the current scale of the problem in the State and some of the steps being taken to remediate it.