New York City’s tap water is frequently recognized for its quality, supplying over one billion gallons daily to more than 9 million people in the city and surrounding upstate communities. This massive undertaking is made possible by a vast, gravity-fed system that begins far outside the city limits. The delivery process relies on a combination of natural protection and sophisticated treatment methods.
Where NYC Water Comes From
New York City’s water supply originates primarily from a massive, protected upstate watershed spanning nearly 2,000 square miles. This system is overwhelmingly supplied by the Catskill and Delaware watersheds, which provide roughly 90% of the city’s water supply. The remaining portion comes from the Croton watershed, located closer to the city in the eastern part of the system.
The geographic distance of the Catskill and Delaware systems, extending up to 125 miles north of the city, contributes to the water’s initial high quality. These watersheds are largely forested and undeveloped, acting as a natural filtration system. The Department of Environmental Protection (DEP) actively manages this land through a comprehensive Watershed Protection Program, which involves land acquisition and partnerships to limit activities that could compromise source water quality.
The entire system comprises 19 reservoirs and three controlled lakes, holding approximately 580 billion gallons of water. This reliance on a naturally protected source distinguishes New York City’s system from many other major cities, which must filter their source water. The Croton system, in contrast, is filtered due to its more suburbanized location and higher level of development.
The Treatment Process
The high quality of the raw water allows the Catskill and Delaware systems to operate under a Filtration Avoidance Determination (FAD) granted by the U.S. Environmental Protection Agency (EPA). This unique status means that most of the city’s water supply is not mechanically filtered but relies instead on stringent disinfection methods to kill pathogens and protect the water during distribution.
The process involves two main forms of disinfection: chlorination and ultraviolet (UV) light treatment. Chlorine is added to kill any harmful microorganisms and prevent bacterial growth within the miles of water mains. The Catskill/Delaware supply also passes through the world’s largest UV disinfection facility, which uses intense UV light to inactivate pathogens like Cryptosporidium and Giardia that are resistant to chlorine.
Additional chemical adjustments are made to prevent corrosion within the system and in homes. Food-grade phosphoric acid is added to form a protective coating on plumbing, which helps prevent metals like lead from leaching into the water. Sodium hydroxide is also added to adjust the pH, reducing the water’s corrosivity. Fluoride is added at a concentration of 0.7 milligrams per liter, a level the NYC Health Department recommends for dental health protection.
Regulatory Standards and Safety Assessments
The city’s water quality is governed by a rigorous regulatory framework that ensures compliance with the federal Safe Drinking Water Act (SDWA), as well as state standards set by the New York State Department of Health (NYSDOH). These regulations establish Maximum Contaminant Levels (MCLs) for a wide range of substances, including heavy metals, organic chemicals, and microbiological contaminants. New York City consistently meets or exceeds these federal and state safety standards.
The Department of Environmental Protection (DEP) maintains this safety record through one of the nation’s most comprehensive testing programs. The DEP performs over 396,000 analyses on more than 33,750 samples from the distribution system annually. An additional 254,000 analyses are conducted in the upstate reservoir watersheds to support the Filtration Avoidance Determination.
This extensive monitoring includes testing for regulated contaminants and emerging concerns like per- and polyfluoroalkyl substances (PFAS). New York State’s maximum contaminant levels for PFOA and PFOS are among the most protective in the country. This volume of testing ensures that any potential issues are identified quickly, providing a scientific basis for the water’s safety assessment.
Addressing Taste and Local Pipe Influence
While the water leaving the reservoirs is of high quality, taste and safety at the tap can be influenced by factors closer to the consumer. The addition of disinfectants like chlorine or chloramines, necessary for microbial safety, can sometimes impart a noticeable taste or odor. This is a common side effect of maintaining a safe residual level of disinfectant throughout the vast pipe network.
A more serious concern involves the quality of the water after it enters private property, often referred to as the “last mile” problem. The city’s water is virtually lead-free upon delivery, but it can pick up lead from older plumbing materials within buildings. Leaching occurs in homes with lead service lines, lead solder, or certain brass fixtures, particularly in structures built before 1987.
The DEP combats this by adding orthophosphate, which creates a protective barrier inside pipes to reduce lead leaching. However, an estimated 14% of service lines in the city are known to be made of lead, and another 15% are of unknown material, posing a risk. Residents in older homes are advised to flush their taps briefly in the morning to draw fresh water and reduce potential exposure from water that has been sitting in the pipes.