Should you use water softener with a septic?

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The water from our drilled well is hard. If I install a water softener, can I run the softener “effluent” into the septic tank with no ill effects?
—Eric Dahlin, via e-mail

With no ill effects? You may be taking your chances. Generally speaking, a water softener shouldn’t hinder the operation of the sewage system if the system has been properly designed under the Ontario Building Code, says Sandy Bos, the on-site sewage system inspector for the Township of Muskoka Lakes and a member
of the board of directors of the Ontario Onsite Wastewater Association. “But every time I see a problem with a backed-up septic, there’s a water softener connected to the system. I think it’s more than a coincidence.”

The case of Water Softener v. Septic System is ongoing. Many studies show that water softeners have no significant impact, but other research is less conclusive. Some of the chief arguments against softeners are that the salt in the backwash (which flushes out accumulated dirt particles) can corrode the tank, interrupt the bacterial action in the septic, and negatively affect the soil in the septic field, and that the volume of water from the backwash is too much for the septic system to handle. So far, science hasn’t quite given us a straight-up “guilty” or “not guilty.”

If you must soften, there are ways to lessen the impact, according to the Ontario Rural Wastewater Centre: Treat only the water you need to soften; use
a newer, more efficient softening device; and have the unit recharge based on water flow, not at regular time intervals, to avoid sending backwash into the system more often than necessary.

Or, avoid the septic system entirely. “Ideally, you wouldn’t direct the water softener backwash into the septic system,” says Bill Goodale, a consulting engineer with C.C. Tatham & Associates who does septic inspections for the Township of Tiny. Instead, have the softening system waste water go into a separate, small leaching pit.