Sewer System


Between your drain and our Wastewater Treatment Plants is an elaborate network of sewers. This network consists of over 7,400 miles of sewer pipes, 152,000 catch basins, and 95 wastewater pumping stations. This complex system quietly does a job we simply can’t live without.

Wastewater & Stormwater

Before we talk about the sewer system, it’s important to understand how we define the different types of water that go into our sewers:


Wastewater is the mixture of used water and waste (sometimes it’s called “sanitary waste” or “sewage”) that flows down the drain or toilet from our homes and businesses. This wastewater is then carried by a series of sewer pipes (these pipes are sometimes called “sanitary sewers”) to the local wastewater treatment plant for further processing.


Stormwater is the rain and melting snow that falls on our rooftops, streets, and sidewalks. Stormwater makes its way into our sewer system through storm drains, or catch basins, located outside of our homes and businesses, usually somewhere along the street. Sometimes the sewer pipes that carry stormwater are called “storm sewers”.

Types of Sewer Systems in New York City

New York City has two types of sewer systems and they are defined by how they handle wastewater and stormwater:

Combined Sewer System

Approximately 60% of New York City has a combined sewer system. This system uses a single pipe or a “combined sewer” to carry the flow of wastewater and stormwater to the local wastewater treatment plant. Managing stormwater in this system can pose challenges because during heavy rainstorms, combined sewers receive higher than normal amounts of stormwater. When flows surpass twice the design capacity of the wastewater treatment plant, a mix of stormwater and untreated sewage flows directly into local waterways to prevent damage to our wastewater infrastructure. These events are called Combined Sewer Overflows.

Separate Storm Sewer System

Approximately 40% of New York City uses a separate sewer system. This system is often referred to as a Municipal Separate Storm Sewer System (MS4). It uses separate pipes to carry wastewater and stormwater. The pipes for wastewater connect directly to the wastewater treatment plant for futher processing, while the pipes for stormwater connect directly to local waterways. Managing stormwater in this system can pose challenges because stormwater picks up pollutants (such as oil, trash, and fertilizers) from the street and carries it directly into local waterways without receiving any treatment.

Stormwater Management

We oversee a broad citywide effort to better manage stormwater in the combined and separate storm sewer systems. These initiatives improve the health of our local waterways and prevent flooding. Visit Stormwater Management to learn more.

Protecting Our Waterways

There are quite a few things New Yorkers can do to help protect our sewers and improve the health of our local waterways: