Westchester's county sewer districts and treatment plants, explained

A Westchester County sewer district is the county-run layer between a town's street mains and the treatment plant, and the county's Department of Environmental Facilities (DEF) manages 13 of them along with seven water resource recovery facilities (Westchester County DEF). Homeowners pay for that layer through a special district line on the property tax bill, and in Mount Vernon through sewer use rates the county sets.

The county describes the route in order. Wastewater leaves the house through the owner's lateral, enters the municipal main, then passes into a "District trunk sewer" and travels by gravity or pump station to a treatment facility. The first piece is private; the second belongs to the city, town or village; the last two belong to the county. The private piece, and where it ends, is the subject of the lateral ownership item.

Districts by municipality

The county's 2026 special-district tax schedule lists districts by city and town; villages appear under their town (Westchester County 2026 tax rates). Names below follow the schedule's wording for each place.

The Yonkers Joint plant

Seven county districts drain to the Yonkers Joint water resource recovery facility. In those districts the county reports owning about 92 miles of trunk sewer, 1,990 manholes and 12 pump stations, serving a population of 509,921 (NYSDEC, Yonkers Joint CSO report for 2024). Mount Vernon's sewage goes there too; the city's sewer plan names the Yonkers Joint plant as its destination. In Yonkers, the county owns the regulators on the city's combined sewers, a split explained in Yonkers sewer laterals.

What the county forbids in its trunk lines

The Westchester County Sewer Act, Chapter 824 of the Laws of Westchester County, reserves the county trunk system for sewage and wastewater. As quoted in a county agreement, it "specifically prohibits the introduction of groundwater, stormwater and excessive inflow and infiltration into the County trunk sewer system" (Westchester County model agreement). Section 824.72 sets "excessive" at more than 150 gallons per person per day for the population a municipality's sewers serve; penalties sit in § 824.77. That pressure flows down to homeowners through local bans on roof leaders and sump pumps tied into the sanitary line and through inflow and infiltration programs.

Background

The county has operated under a state Department of Environmental Conservation Order on Consent since 2004, amended in 2008, that requires reducing inflow and infiltration. Under it, the county drafted a model agreement asking Long Island Sound municipalities to finish sewer evaluation studies and maintenance programs in 2016 and 2017 and to propose point-of-sale lateral laws. Which towns signed was not confirmed. A pending state bill, S7927-A, would let New Rochelle, the Town of Mamaroneck, Larchmont and Pelham Manor convey or lease their sewer systems in the New Rochelle district to the county; its status was not confirmed (NY Senate).

Key facts

• DEF manages 13 sewer districts and seven treatment facilities (Westchester County DEF).
• Route: owner's lateral, municipal main, county district trunk sewer, treatment plant.
• Seven districts flow to Yonkers Joint, with about 92 miles of county trunk sewer and 12 pump stations (NYSDEC).
• The County Sewer Act (Chapter 824) bars groundwater and stormwater from trunk sewers.
• Excessive inflow and infiltration means over 150 gallons per person per day (§ 824.72).

Sources

• Westchester County DEF: the Wastewater and Water Division
• 2026 Special District Tax Rates, Cities and Towns (Westchester County)
• NYSDEC SPDES NY0026689 annual CSO report, 2024
• County model agreement quoting the Sewer Act, archived file
• NY Senate Bill S7927-A text