Road salt is leaching into the reservoirs that hold New York City’s tap water and could make some of it unhealthy to drink by the turn of the century, according to a new study commissioned by city environmental officials.

The study, released last week by the city’s Department of Environmental Protection, found that while salt was edging upward throughout New York’s vast watershed, it was especially pronounced in the New Croton Reservoir, just north of the city.

In that supply, which provides about 10 percent of the city’s drinking water, levels of chloride — a chemical found in salt and an indicator of salinity — tripled over the last 30 years.

If the trend continues, drinking water from the New Croton Reservoir may not meet current safety standards by 2108, according to the report.

While road salt is a main driver of salinity levels in drinking water throughout the United States, other contributing factors include wastewater treatment plant discharges and agriculture, according to the report. Elevated salt levels in fresh water can contribute to health issues like high blood pressure and can also damage the ecosystem, the study said.

Reducing salinity levels throughout New York City’s water system should start with more prudent use of road salt, said Rohit T. Aggarwala, the head of the environmental protection department, which manages the water supply and commissioned the report.