Over the past several months, as we’ve investigated road salt pollution in homeowners’ water, we’ve been keeping an eye out for lab tests that show salt getting into town and village water supplies.

It stood to reason that since road salt can run off roads into private wells, it could also get into water supplies used by larger public drinking water systems.

But tracking the spread of salt is complicated because of uneven testing by public water systems across upstate New York. The state’s Department of Health decides which contaminants public water suppliers have to test for each year.

In interviews with local water officials from across the region over the past several months, some struggled to remember how often they had been asked to test for salt.

But in November, for the first time in a decade, the Village of Saranac Lake had to test for sodium and report those results to the public in the village’s annual drinking water quality report. That report is just recently being made public.

What it found was troubling: elevated sodium levels, which would suggest contamination from several possible sources, including road salt.

As I wrote in a story last week, the tests didn’t find other major problems —no repeated signs of bacteria or other toxins— and the water remains safe for most people. But federal guidelines recommend that people on severely restricted sodium diets avoid drinking water with more than 20 milligrams of sodium per liter of water. The village’s water has 53 milligrams. (Someone would have to drink nearly a gallon of such water to get the same amount of sodium as a serving of Lay’s potato chips.)

The last time Saranac Lake reported testing for sodium was September 2006. Back then, Saranac Lake was getting water from a completely different water source, McKenzie Pond.

But water quality regulators have soured on lakes and ponds as water sources for the public, because they are exposed to contamination and runoff. So regulators began to give water districts a choice: install an expensive water filter to clean up lake and pond water or switch to groundwater.

Saranac Lake switched to groundwater rather than pay to filter McKenzie Pond water.

Now, we’re dealing with a big what if: What if the groundwater could also be contaminated?

Nationally, groundwater gets messed up all the time. But Adirondack water is expected to be pristine.

Presumably, the village’s groundwater supply was tested at the time of the switch for sodium and every other possible contaminant. Last we checked the village was still looking for the results of those tests, which it could use to see if there was salt there to begin with, or if something has changed.

Dan Kelting, the head of the Adirondack Watershed Institute of Paul Smith’s College, said if the village’s recent test results were accurate, they showed a “remarkable level of contamination.” But he thinks the signal of salt is so strong there’s something else going on, perhaps a problem with the sample or the lab results.

At least two village officials, including the long-time water system operator, have said they want to figure out what’s happening, but it’s not clear yet if the village will go ahead with the tests required to get to the bottom of the problem.

Generally, salt can fly beneath the radar: There are other water systems in the country that are used by many more people and have much higher sodium levels. Phoenix, for instance, can have water four times as salty and San Diego can have about twice as much salt in its water as the tests for Saranac Lake show. But both those cities get water from sources that are expected to be salty. Adirondack water is not expected to be salty.

So salt showing up in drinking water systems would be a problem for several reasons: It suggests that road salting, some of it by the state and some of it by local towns and villages, could be fouling up the very waters that the Adirondack economy has come to depend on.

As we’ve reported, the village wouldn’t be alone in seeing some possible traces of road salt in its water supply. Two other public water systems in the Adirondacks also had evidence their water was being contaminated by salt, but one of those systems only served a highway garage and the other switched water supplies for other reasons.

If Saranac Lake’s issue isn’t road salt or a lab error, another possible source of such contamination is sewage, either human or animal waste, and if that’s in the water, that’s a bigger problem.