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 water softener.
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 – or the increased amount of water entering into the system – may be harmful and possibly cause septic systems to fail. Although there is no scientific data available that supports harmful effects, there have been many investigations into the potential for problems to occur.
The Effect of Sodium Salt on Septic Systems
Common knowledge supports that higher levels of sodium salt can have a direct impact on bacterial life forms. For instance, most bacteria usually found in fresh water ecosystems would be unable to live in a high salinity environment like an ocean. For this reason, concern was generated that septic systems that rely so heavily on bacterial action may be effected by high concentrations of sodium.
These concerns seem to be unwarranted. First, a typical residential sized water softener discharges between 40 and 70 gallons of water per regeneration. Through much of the regeneration process, fresh water is discharged, containing no salt at all, so the total concentration of salt is very dilute. However, during some stages of regeneration, the sodium concentration can reach as high a 5,000 to 10,000 ppm for brief periods of time.