Troubleshooting: Water Softener Use and Garbage Disposals

These two major water-using devices can wreak havoc on onsite systems

From a troubleshooting standpoint, another conversation to have with the homeowner focuses on two major water-using devices that can cause problems: water softeners and garbage disposals.

Over the past decade there has been a lot of discussion and research on whether water softeners have an impact on septic systems by changing soil structure in the drainfield, reducing infiltration capacity and leading to early failure. Early research done in the late ‘70s and early ‘80s indicated there was no significant effect. More recent research has indicated that there may be problems with soils already high in sodium content and in low exchange capacity soils.

For the 30-some years I was with the University of Minnesota, we recommended to our installers they route the softener backwash to an area other than the drainfield. The other area could be a separate trench just for the backwash or to the surface away from the residence, not near the drainfield and not onto a neighbor's property.

The other potential problem with softeners is dependent on the hardness of the water and the number of times it is set to recharge, which can deliver a large amount of water to the drainfield. This, coupled with the potential for timers and valves sticking and homeowners not paying attention to maintenance requirements, just adds to the reasons that flow should be directed somewhere other than the drainfield.

One other note: the solution is not to tell the homeowner not to have a softener, but instead to get them to change the location of the discharge. They have a softener due to problems with their water. It takes more water and soap to get things clean if you have hard water. So, if you take out the softener, their water use will likely not decrease, which is the objective.

Finally, the garbage disposal — depending on how it is used — can deliver large amounts of water to the system; but even more than that, the solids delivered through the disposal are often ground so fine that they don’t settle well in the septic tank. Often bone fragments and other materials that do not break down or are harder to break down in the septic tank are delivered.

In addition, delivery of the organic material to the tank can increase the BOD of the effluent delivered to the drainfield. This additional BOD can lead to the development of a more resistant biomat, resulting in a decrease in the long-term acceptance rate for the drainfield.

Presence of a garbage disposal means septic tank cleaning should be more frequent due to increased solids accumulation. To avoid problems, including the extra water, the recommendation is to not have a disposal. This will be a problem with some homeowners, but talking with them in terms of saving future expense in drainfield replacement is usually helpful.

About the author 
Jim Anderson is connected with the University of Minnesota onsite wastewater treatment program and is an emeritus professor in the university’s Department of Soil, Water and Climate. Send him questions about septic system maintenance and operation by sending an email to

This article is part of a series on troubleshooting onsite systems:


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