Are water softeners septic safe?

A water softener cleans itself with salty water, called brine, and that water has to go somewhere. In many rural homes, it goes into the septic system. Whether that's a problem depends on who you ask, so we've set out both sides.

What's the evidence that softeners are safe?

The Water Quality Association, a trade group for the water treatment industry, argues that efficient softeners cause no harm and may even help. Its 2019 paper cites:

• A 1978 NSF study that found no harm to home aerobic units
• A 1978 University of Wisconsin study that found no harm to tank bacteria or soil percolation
• A 2013 Virginia Tech study that found efficient softeners improved settling, while very inefficient ones produced poorer effluent

Virginia's health department took a similar line in a 1994 memo: discharge shouldn't harm a drain field up to 60 gallons per regeneration and 180 gallons a week.

What's the evidence that softeners cause problems?

Rhode Island's environmental agency doesn't ban the practice, but it doesn't recommend it either. It says brine can disturb settling in the tank and cut the room available to separate solids, which may let solids reach the leach field. Makers of the most common alternative systems there, it adds, prohibit or advise against brine.

The University of Minnesota says softener recharge water "does not need to go in the septic system." And in a 2007 commentary, an engineer at a treatment system manufacturer argued that brine harms both tanks and fields. His evidence was largely field observation, and his employer sells such systems.

What do both sides agree on?

Extra water is a concern. The Minnesota Department of Health says softener discharge could overload a system that's undersized or near the end of its life.

How can you reduce the risk?

• Set the softener to your actual water hardness and iron level.
• Regenerate no more often than you need to.
• Bypass the softener when you're away for a long time.
• Fix leaks, and keep sump pumps and roof drains out of the system.
• Have an existing system inspected, and consider an effluent filter on the tank.
• Pump more often if a professional advises it. Rhode Island suggests this if brine goes to the tank.

Where can softener brine go instead?

That's a local question. Indiana lists approved points that include the building sewer, a point after the tank, or a separate absorption field. Rhode Island prefers a below-ground drywell. Minnesota's rules for its noncommunity water systems allow certain soil or surface discharge, but set distances from wells. Don't assume another state's option is allowed where you live.