March 21, 2025

Croton System Chloride Levels Have Tripled in the Last 30 Years and Could Exceed Maximum Salinity Levels By 2108; Road Salt and Human Activities are Key Contributors

Minor Salinity Impacts in City’s Larger Reservoirs Throughout the More Sparsely Populated Upstate Catskills Region

The New York City Department of Environmental Protection (DEP) today released a new, comprehensive study on rising salinity levels in the City’s water supply, which show salinity levels in the Croton System reservoirs—one of the City’s primary water sources—have been steadily rising due to road salt runoff and other human activities. If the trend continues, the New Croton Reservoir could exceed the State’s maximum allowable chloride levels at the turn of the century. Salinity levels in the system’s main New Croton Reservoir have tripled in just a 30-year time frame.

The study also found that the City’s main reservoirs in the rural Catskills region further upstate have low levels of salinity; those salinity levels are also increasing, but at a much slower rate.

DEP’s “Salinity Management Assessment” study reviewed nearly 33 years of data and found steadily increasing salinity levels in all 12 reservoirs and three controlled lakes in the water supply’s Croton System, the oldest and smallest of the reservoir systems which typically provides about 10 percent of the City’s water supply. All of the Croton System’s reservoirs and lakes throughout Westchester and Putnam counties feed into the New Croton Reservoir about 22 miles north of the city line. The study found that at the current rate of increase the New Croton Reservoir would reach the state’s maximum contaminant level for chloride, a main component of salt, by the year 2108.

High levels of salinity in fresh water supplies can impact human health by contributing to high blood pressure and hypertension and can also significantly impact watershed biodiversity and ecosystems with potentially detrimental impacts on water quality.

“Our study found a clear and troubling trend of increasing salinity in and around the Croton water supply region,” said DEP Commissioner Rohit T. Aggarwala. “As the nation’s largest municipal water supply system serving half of the state’s population with the gold standard in water quality, we must do everything possible to protect this most precious resource. It is imperative that we work closely with state and local governments, and our environmental partners, to develop and implement policies to slow and hopefully stop this trend.”

“We thank DEP for their partnership in taking action to safeguard the health of our ecosystem and our communities,” said Riverkeeper President and Hudson Riverkeeper Tracy Brown. “The problems identified in the Croton watershed are unfortunately common statewide, and we must use the stark findings in this report to address the issue statewide. Now is the time for smarter use of road salt and the equipment upgrades that will protect our friends, family, and neighbors with high blood pressure, and those on low sodium diets, throughout New York. This is also critical for ecosystem and human health as salt changes water chemistry, leading to increased risk of lead leaching from pipes that carry drinking water, other heavy metals being mobilized from source waters, and the formation of Harmful Algal Blooms.”

“Millions of New Yorkers, including many of my constituents in Northern Westchester and Putnam County, are impacted by rapidly rising salinity in the East of Hudson Watershed, which affects their source of clean water,” said New York State Senator Pete Harckham, Chairman of the Senate Committee on the Environment. “In less than 30 years, the Amawalk Reservoir will exceed the maximum allowable levels for salt. Once contaminated, it could take decades for the reservoir to return to acceptable levels. All levels of government must work collaboratively and with all deliberate speed to protect our precious drinking water.”

“DEP’s findings should be a wake-up call to anyone who thinks our water supply is immune to environmental degradation,” said New York State Assembly Member MaryJane Shimsky. “Looking at the increase in salinity over the past 40 years, we know that the New Croton Reservoir’s water will no longer be safe to drink by 2108 unless changes are made. We must take the corrective steps needed to protect this resource, and we must do it right away. If we don’t, the damage to our residents, agriculture, and wildlife will be irreversible; and the cost of replacing our water infrastructure far more expensive.”

By analyzing data from 1987 through 2019, DEP found a sustained increase in chloride concentrations in all of reservoirs serving the water supply system, though the City’s largest reservoirs in the Catskills showed only negligible increases and contain relatively low levels of chloride. This is not unexpected given the lower population, pavement and property parcel densities in that region, though the study includes recommendations to help protect those reservoirs in the future.

The study found winter de-icing of roadways and parking lots, wastewater treatment plant discharges and private water softening systems as likely main contributors to increased salinization. Water filtration plants cannot remove salt from water. Instead, salinity can only be reduced through a costly and heavily energy dependent desalinization process.

Recommendations to reduce salinity included supporting stakeholder efforts to develop best practices for reducing man-made salinity contributions throughout the water supply region, expanding studies on specific sources, and building public and stakeholder awareness to the trends and impacts of salinity infiltration of fresh water supplies.

DEP manages New York City’s water supply, providing more than 1 billion gallons of high-quality drinking water each day to nearly 10 million residents, including 8.8 million in New York City and 1 million more in counties north of the City. The water is delivered from a watershed that extends more than 125 miles from the City, comprising 19 reservoirs and three controlled lakes. Approximately 7,000 miles of water mains, tunnels and aqueducts bring water to homes and businesses throughout the five boroughs, and 7,500 miles of sewer lines and 96 pump stations take wastewater to 14 in-city treatment plants. DEP also protects the health and safety of New Yorkers by enforcing the Air and Noise Codes and asbestos rules. DEP has a robust capital program, with a planned $37 billion in investments over the next 10 years. For more information, visit nyc.gov/dep, like us on Facebook, or follow us on X, formerly known as Twitter.