Greenspace: Is your water softener too salty?

August 5, 2018

Minnesota’s water is getting salty.

Rising salt levels in Minnesota’s freshwater is an ongoing struggle, one commonly attributed to the use of salt to de-ice roads. A recent University of Minnesota study, however, points to household water softeners as another major culprit.

According to the study, household water softeners introduce approximately 140,000 metric tons of salt into Minnesota’s environment per year in the form of chloride. That’s about a third of the 400,000 metric tons contributed by road salts, making water softeners the fourth-greatest contributor of salt to Minnesota’s freshwater.

So far, southeast Minnesota has avoided excessive buildup of chloride in freshwater sources. Chloride can be toxic to aquatic life. But for David Lane, environmental manager of Rochester’s Water Reclamation Plant, high chloride levels are a familiar issue.

Salt in the Zumbro

Rochester’s reclamation plant doesn’t treat or remove chloride, a process that is difficult and expensive. Instead, Lane uses frequent testing to monitor chloride levels in the water.

According to the most recent test, taken July 9, the chloride level for water entering the plant was 272 parts per million and, the level in water discharged into the Zumbro River was 269 parts per million.

That’s well above the Minnesota Pollution Control Agency’s water quality standards for chloride, which are set at 230 ppm.

The numbers seem bleak, but Lane says the Zumbro River isn’t in imminent danger of being impaired. The MPCA’s standards apply to chloride levels in the entire body of water, not direct outflow from treatment plants. Once diluted in the Zumbro River, the chloride concentration drops significantly. Downstream sampling from July 9 showed a chloride level of just 50 ppm.

That’s good news, both for the river and the reclamation plant, but Lane says they don’t want to assume those low levels will stay that way.

“We want to try to give ourselves as much of a safety buffer as possible,” he said. “The downstream monitoring shows there’s not an issue. We want to make sure it stays that way.”

Where does it come from?

Since the reclamation plant receives wastewater only from Rochester’s sanitary sewers, any chlorides entering the plant come from something other than road salt. Currently, that seems to be water softeners, but there are reasons for that.

First, Rochester’s water is very hard. At 17 grains per gallon (a measure of hardness), water softeners have to use more salt to properly soften water for household uses, which puts more chloride in wastewater.

Second, and more significantly, residents using old or poorly tuned softeners use more salt than necessary. Inefficient softeners or softeners not properly tuned to the hardness of the water may regenerate or renew the brine solution used to remove calcium and magnesium from hard water, again raising the amount of chloride released into wastewater.

Proper tuning, Lane says, can make a huge difference to chloride levels. Where an old or poorly tuned softener might use as much as 25 bags of salt per year, a newer, well-tuned one might need only five bags.

Even a new softener can overuse salt if it isn’t properly tuned to the hardness of the water. Brand new softeners default to the hardest setting (30 gpg), which Lane says is “overkill” for Rochester’s conditions.

“Kind of the two big messages we say is either to replace your older water softener with a newer, more efficient one, or at least have it tuned up so it operates more efficiently and uses less salt,” Lane said.

Salting with care

Those messages will eventually be part of the reclamation plant’s chloride management plan. The plan is a work in progress, since Lane says the plant only became aware of the high chloride issues within the last few years.

In addition to developing strategies to help residents reduce their chloride contributions, Lane intends to focus on identifying sources, both in residential areas and industries. Management efforts will also include continued monitoring of the river to assess downstream impact.

“There’s a lot of unknowns right now,” Lane said. “The question has been raised, and we’re just starting to work on that issue.”

Although plans are being developed to combat future chloride contamination, it’s not an issue Lane expect will ever entirely go away.

“It’s getting a lot more attention in Minnesota because Minnesota is one of those places where we have that kind of unique combination of hard water and our roads are pretty icy in the winter and we have a lot of lakes and streams around,” he said. “You put those three together, and that’s why Minnesota has this issue.”

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