Skip to main content

Filtration Avoidance and the Catskill/Delaware System

Filtration Avoidance and the Catskill/Delaware System 

Under the Surface Water Treatment Rule (SWTR), a drinking water system may qualify for filtration avoidance if it meets strict criteria. The system must not be the source of a waterborne disease outbreak, must comply with source water limits for coliform and turbidity, and meet maximum contaminant levels (MCLs) for coliform and total trihalomethanes. It must also maintain disinfectant residuals, provide redundant disinfection capability, and implement a comprehensive watershed control program. This program must: 

  • Characterize watershed hydrology, land use, source water quality, and operations. 
  • Identify, monitor, and control manmade and natural activities that threaten water quality. 
  • Demonstrate enforceable control of activities through land ownership or formal agreements. 

Catskill/Delaware System

The U.S. Environmental Protection Agency (EPA) determined in January and December 1993 that New York City’s Catskill/Delaware water supply met the criteria for filtration avoidance. The December 1993 Filtration Avoidance Determination (FAD) imposed more than 150 conditions related to watershed protection, monitoring, and studies. 

Implementation proved challenging. New York City was unable to secure a land acquisition permit, gain approval for revised watershed regulations, or upgrade wastewater treatment plants (WWTPs) outside city limits—measures critical for reducing contaminant and nutrient discharges. By 1996, EPA Region II concluded that the city had not fully demonstrated its ability to sustain a strong watershed protection program and could not renew the FAD without further assurances. To resolve these issues, New York State convened negotiations among NYC, the State, EPA, watershed communities, and environmental organizations. 

Filtration Avoidance Determinations (FADs)

Despite early challenges, the Catskill/Delaware system has continued to meet the criteria for filtration avoidance. EPA and the New York State Department of Health have issued FADs at key intervals: 

  • EPA: January 1993, December 1993, January 1997, May 1997, November 2002, July 2007 
  • NYSDOH: Revised 2007 FAD, followed by the 2017 FAD (issued December 28, 2017) 

Each determination documents the city’s progress in watershed protection and outlines conditions for continued compliance. These ongoing efforts ensure that the Catskill/Delaware portion of New York City’s water supply remains unfiltered while still meeting all public health and regulatory standards.

Learn more on the EPA Website.

EPA Website