Rising Salt Levels Threaten New York City’s Water Supply

New York City authorities are sounding the alarm over rising salinity in the suburban reservoirs that provide 10% of the city's celebrated drinking water. The Croton Water System, which has been supplying the city with water since 1842, is seeing rising salt levels from decades of road salt use, sewage treatment plant outfalls, and water softeners. A new study cautions that if unchecked, the trend would render the Croton system unusable as a source of drinking water by 2100.

The problem had been worsening over the years at a steady pace. Chloride levels in the system's primary reservoir, which is roughly 20 miles north of the city, have increased threefold from 1987 to 2019. The research estimates that the levels of chloride will exceed New York State's maximum contaminant level by 2108, rendering the water supply unsafe for drinking. Although Croton reservoirs supply only a small percentage of New York City's water, approximately 10%, they play a vital role in providing a stable supply for millions of inhabitants.

New York City's tap water has been prized for generations for its cleanliness and flavor, described as the "champagne of tap water." The city draws most of its water from the Catskill and Delaware watersheds to the west of the Hudson River, which are relatively less subject to salinization due to lesser urban development. But the Croton system serves not only the city but also more than a dozen municipalities to its north, so the issue is not strictly a city problem. If the reservoirs become too salty, local governments will have to seek new sources of water as well.

Road salt is one of the principal causes of the increasing salinity. Each year, millions of tons of rock salt are applied to roads in the United States to inhibit the formation of ice and minimize accidents. Though it is effective in maintaining road safety, the salt ultimately finds its way into waterways, spiking chloride levels in reservoirs and lakes. The issue is prevalent throughout the northeastern and midwestern United States, where the use of road salt is routine. According to Shannon Roback, science director for the environmental group Riverkeeper, elevated salt levels in drinking water raise environmental concerns and can be harmful to individuals on low-sodium diets.

New York City's commissioner of environmental protection, Rohit Aggarwala, added that the Croton Water System is headed toward obsolescence unless something is done about it. He added that by the year 2100, the reservoirs might be used as recreational facilities but would not be sustainable for use as drinking water. Although the city has choices to help resolve the issue, they all present challenges.

One option is to strip salt from the water with reverse osmosis, which is an effective but costly and energy-hungry technology. Another option is to mix water from the Croton system with lower-salinity water from the Catskill and Delaware watersheds. That would not assist the municipalities that use only Croton water. The most feasible solution, officials maintain, is to decrease the use of road salt in the area. This might include encouraging state and local road crews to switch to alternative de-icing technologies, equipping plows with sensors to monitor road temperatures, or optimizing application rates to avoid unnecessary salt.

State Senator Pete Harckham, whose district includes the impacted area, characterized the study's conclusions as disturbing but not surprising. Numerous community wells in the area have already been shut down for having too high a concentration of chloride. Harckham is sponsoring the legislation to try to solve the problem, such as a bill that would direct additional studies of the effects of road salt in the Croton watershed. He emphasized the necessity for state and local governments and agencies to come together to address the issue before it gets any worse.

The problem of road salt contamination is not limited to New York. Several lakes and reservoirs throughout the U.S. have experienced increasing salinity, which has raised concerns about long-term water quality. While some research indicates that salt levels can stabilize at levels below the toxic threshold in some water bodies, others caution that ongoing use of salt will make some water supplies unusable.

Aggarwala and other officials hope to take action before the Croton system gets to that point. In order for New York City to be able to maintain the purity of its water for generations to come, drastic changes need to be made to how winter road maintenance is carried out in the area. Lowering road salt usage is a multiagency effort, but if nothing is done, one of the city's essential sources of water may be lost in decades.