There are over 20 million households in the United States currently using on-site septic systems, and that number appears to be growing. We get many questions from our customers as to what effect (if any) water softener discharge has on a these systems. With such a wide range of information and opinions available, we felt that it was appropriate to examine some of the studies on this topic, and try to accurately present an overview of current understanding.

The Septic System and Water Softening Process

Septic system function is very straightforward. Your homes plumbing is piped into a in-ground storage tank. When wastewater enters this tank, the heavier solids settle to the bottom. Bacteria present in the storage tank digest the solids, breaking it down to a liquid. After this process is complete, relatively clear water is discharged from the primary tank into a second holding tank or distribution box. Water then re-enters the surrounding soil through a drainage field consisting of perforated underground piping.

The water softening process is accomplished by a chemical cation exchange that replaces the calcium and magnesium in your water with a equivalent number of sodium or potassium ions. During the softening process, your household water passes through the resin bed, and the magnesium and calcium contained in the water are removed. A given sized resin bed has a fixed capacity to remove hardness before it needs to be regenerated to full capacity in order to continue to provide softened water (for example, one cubic foot of resin has the ability to remove 32,000 grains of hardness from your water). When the resin bed is nearing exhaustion, the control valve washes the resin bed, and draws salt containing solution from the brine tank through the resin. As the salt contacts the resin bed, the process of ion exchange occurs, and the magnesium and calcium (hardness) that was collected in the bed during operation is washed to drain. After a final rinse to remove the excess salt, the resin bed is again ready to provide softened water.

The concern of discharging water softeners into an on-site septic system arises out of a belief that sodium salts used by water softeners during the regeneration stage