Many of us have never given it much thought, but where exactly does all the salt sprayed on roads go every year?

Well, it turns out that much of it is washing into rivers and lakes, and subsequently radically altering its chemistry. This is not only bad news for the wildlife in them, but also for the millions of people who rely on these sources for fresh drinking water.

After studying streamwater data from 232 places across the United States, and publishing the results in the Proceedings of the National Academy of Sciences, researchers found significant increases in the salinity of the water at 37 percent of sites. In some places, they found that alkaline levels – a measure of the salinity – increased by a massive 90 percent over the last 50 years.

This is thought to be in large part due to agricultural runoff, particularly in the Midwest where heavy fertilizer use is prevalent. However, it is also due to the large amount of salt that is spread on the roads during winter. This has led to sharp chemical changes in many of the country’s major rivers, such as the Hudson, Mississippi, and Potomac Rivers.

One worry is what effect the changes in the chemical composition of the water can have on the health of those drinking it. The Flint water crisis was due to the town switching water sources to the Flint River, which had a higher salt concentration than their original source. This corroded the insides of the pipes in the town, causing the lead in them to leach into the water supply.

This means the findings of this study could have major implications on how regions manage their freshwater and regulate the use of salt on their roads.

“Many people assume that when you apply salt to the landscape, it just gets washed away and disappears,” explains lead author Sujay Kaushal of the University of Maryland in a statement. “But salt accumulates in soils and groundwater and takes decades to get flushed out.”

There are a variety of ways in which the impact of this can be lessened. For one, the salt spread on roads could be wet first to allow it to stick, or brine could be used to prevent ice from forming on roads. The researchers also suggest a system of sensors on roads and pavements so that salting can be better targeted. Building further away from water catchment areas will also help. It would also be useful if sewage drainage systems were simply better designed and aging pipes replaced with safer alternatives.