NYC Sewer System

NYC’s Sewer System

All across New York City, combined-sewer systems (CSS) are used to collect sewage, storm water, and industrial waste. All of this effluent flows through one pipe — hence the name combined sewer system. Approximately 70% of city sewers are combined. On a typical day, the CSS can hold all the matter that flows through its pipes. However, when rain is heavy or when snow begins to melt, the CSS begins to fill with the storm water. The mix of the storm water and waste begins to rise until the CSS reaches capacity. When the CSS exceeds capacity, all the waste– untreated — is offloaded directly into the water. This is combined sewage overflow (CSO).

Combined Sewer System

A closed sewer system (CSS) leads to combined sewage overflow (CSO). Photo credit: U.S. Environmental Protection Agency


Table of Contents:


o CSO in NYC
NYC Sewer System
Combined Sewer System
Eliminating CSO

o Drinking Water in NYC
Buried Streams

o Holland

o Water Around the World

o PLANYC Initiatives

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