All NYC residences receive drinking water from a public water system. Most water is gravity fed from a network of reservoirs and lakes in protected watersheds, up to 125 miles from the city.

The NYC water system consists of two surface water systems: Croton and Catskill/Delaware and one groundwater system, in Southwestern Queens. Since 1999, the Croton system has served as a supplemental water system. The Catskill/Delaware reservoir system supplies almost all NYC drinking water. For more on how NYC gets and tests its water, read the 2022 Drinking Water Supply & Quality report.

We display data on disinfection by-products, nitrates, and arsenic in NYC drinking water because these contaminants occur most frequently at levels that may be of public health significance in drinking water nationwide.

Drinking Water Quality and Health

The New york Department of Environmental Protection (DEP) regularly samples, analyzes and reports contaminant levels at the source and in the drinking water distribution system. Monitoring drinking water is important because contamination in a single system could exposes many people at once. People can be exposed to contaminants in many ways besides drinking the water. They can also be exposed through eating food prepared with the water, breathing water droplets or chemicals released from the water while showering, or by absorbing chemicals through their skin while bathing.

Lead: According to the DEP, drinking water enters the NYC water system “virtually lead-free.” The DEP then uses anti-corrosion methods to reduce the leaching of any lead that may be present in plumbing fixtures, solder, or pipes, which connect the water system to buildings in NYC. Federal regulations require that lead testing of water is done at the tap of a sample of NYC buildings each year.

Disinfection by-products: Drinking water is disinfected to reduce the possibility of illness from microorganisms. Disinfection by-products (DBPs) are chemicals that can form when a disinfectant such as chlorine reacts with naturally occurring organic matter and other substances in the source water. Current research is looking at whether there are health effects from chronic exposure to the by-products of water disinfection.

Nitrates: Nitrates are commonly found in water near where nitrogen-based fertilizers are used. Decades ago, it was discovered that infants who were fed formula made with water containing nitrates over 10 mg/L sometimes became seriously ill, due to the interference of nitrate with the oxygen-carrying capacity of blood.

Arsenic: Arsenic is naturally occurring in groundwater systems in some parts of the US. It may also enter drinking water systems through past use of arsenic-containing pesticides and wood preservatives. Chronic exposure may increase risk of certain cancers. It is not detected in NYC drinking water.

About the Data and Indicators

The data presented here provide summary measures of contaminants in drinking water sampled at many points in the distribution system.

Prevention

• Most people do not need to take any actions to prevent water-related illnesses or health effects from drinking NYC water.
• Though levels of contaminants are consistently very low in water that arrives to a building, lead or lead-soldered plumbing in some older buildings may raise lead levels in water at the tap. Reducing the possibility of exposure to lead in drinking water is simple and inexpensive. Run your tap for at least 30 seconds, until the water is noticeably colder, before drinking, cooking or making baby formula. Free tap water quality tests are available by calling 311.
• Ultimately, maintaining the highest quality drinking water depends on protecting our lakes, rivers and aquifers from contamination.

Key Messages

The quality of the drinking water in the NYC system is excellent. The water systems serving NYC are consistently in compliance with EPA guidelines.

DBP concentrations show a seasonal effect with higher concentrations during the warm and rainy months when more organic material is in the water systems. Arsenic levels are consistently very low in NYC. Nitrate levels are also consistently low, owing to the protection of upstate watersheds from farm runoff.

NYC drinking water has many advantages over bottled water or processed beverages. Its sources are known, and its purity is checked. It is not stored in plastics, and it doesn’t get shipped in vehicles that pollute the air. It costs little or nothing, and it is calorie-free.

There are many schemes of neighborhood boundaries (or geographies) available for different datasets. These include:

• Citywide
• Borough
• United Hospital Fund 42 (UHF42) and United Hospital Fund 34 (UHF34) neighborhoods
• Community Districts (CD), and, related, Community District Tabulation Areas (CDTA)
• Public Use Microdata Areas (PUMA)
• Neighborhood Tabulation Areas (NTA)

We try to make data available at as fine a geographic resolution as we can. Read more about different geographies at this data story.

It would be convenient if each dataset could be made available at the same geography, but this is not always possible. The neighborhood boundaries available depend on the specifics of the underlying dataset.

When we have multiple years of data, we show the data as trend charts.

Trends for individual neighborhoods tend to be very unstable (or "bouncy"), due to small counts for outcomes in individual neighborhoods. To show clearer trends, we usually aggregate up and show trend data by Borough.

Options on some indicators let you compare this indicator to other similar indicators.

We try to make data available as soon as we can.

Many datasets take a long time to reach us — a "lag" of several years, during which data are gathered from different entities to try to create a complete dataset; data are processed (cleaned, deduplicated, etc), and analyzed. It can take several years to prepare a dataset — so a dataset that is several years old is sometimes the most up-to-date information available. Still, this data continues to show us valuable trends and insights.

We also try to display datasets that have been available for many years. Some datasets (like those that are asked on surveys) are not asked every year of the survey, which means that we cannot provide annual data.

For some datasets, we have to aggregate time periods in order to break down data by borough or neighborhood.

Measures are the numeric ways that a dataset (or indicator) are expressed. Examples of different measures might be: number, percent or rate.

A number tells us how much of an outcome is in a certain area. But a rate (usually expressed as, for example, 40 per 100,000) tells us how much of an outcome there is, relative to the population of the area in question. This lets us compare neighborhoods of different sizes.

On this site, we try to show how environmental factors might be connected to health outcomes. One way we do this is with Correlates. We choose potentially-related datasets and display them on a scatterplot so you can see how these two datasets are correlated.

The Disparities view displays neighborhoods by poverty category to show underlying disparities in the data.

Read more about correlation here.