In New York City, stormwater is conveyed through combined sewers or separate sewer systems. In unsewered areas, water flows directly over the ground into waterways.
Combined Sewer Areas
In most areas of the City, sanitary and industrial wastewater, rainwater and street runoff are collected in the same sewers and then conveyed together to the City's treatment plants. This is known as a combined sewer system. Approximately 70 percent of the City sewers are combined.
Separate Sewer Areas
In some New York City neighborhoods, sanitary waste and stormwater runoff are channeled in separate sewer systems: sanitary waste is carried to wastewater treatment plants while stormwater is channeled directly to local streams, rivers, and bays.
In unsewered areas, such as parks and wetlands, this water is absorbed into the ground or channeled into waterways.