ST. PAUL  — Home water softeners are sending a significant amount of salt into Minnesota’s lakes, streams and groundwater, according to a new study from the University of Minnesota.

About 50 of the state’s water bodies have chloride levels that exceed its water quality standards reported. Excess chloride can be toxic to aquatic life, corrode bridges and infrastructure and change the taste of drinking water.

University researchers from the Water Resources Center created a chloride budget to estimate how much salt enters the environment each year from various sources.

Road salt was the largest source of chloride statewide, contributing more than 400,000 metric tons (440,900 tons) annually to the environment. The study ranks household water softeners as the fourth largest source, contributing about 140,000 metric tons (154,300 tons) of salt per year.

“I think it will be surprising to a lot of people because we’ve been talking about road salt, road salt, road salt,” said Sara Heger, a research engineer with the center. “A lot of people don’t think about that their softener in their home is like that road salt — or that we’re another source.”

Salt from water softeners can enter the environment through municipal sewer systems and septic systems, Heger said.

Homes connected to municipal sewer systems send chloride from water softeners down the drain, which ends up at the wastewater treatment plant. Homes that bypass the water treatment system with septic systems send the salty water into the soil, eventually traveling into the groundwater.

Commercial fertilizer and manure are also major sources of salt, according to the study. But Heger said they may have less impact on water quality because they’re spread over a large area.

The state estimates about 100 of its wastewater treatment plants are discharging more chloride than allowed by state standards.