There has been some anecdotal evidence that sodium added to septic systems by a water softener may have negative effects on the ability for the drain field soil to percolate properly.
Many studies have been performed to investigate this issue (2,4,6), and seem to indicate that water softener regeneration discharge does not interfere with drain field percolation, but may actually improve percolation in finely textured soils. This may be due to a higher calcium concentration found in softener regeneration discharge. When this “calcium rich” water enters the drain field, it sometimes increased the porosity of the soil (dependent on the type of soil present), improving the percolation process. To further support this finding, gypsum, another calcium rich material, has long been used for this same purpose.
Conclusions and RecommendationsThe results of our review are corroborated by a fact sheet published by the Environmental Protection Agency(5), that points out the following:
a) High concentrations of calcium and magnesium in the softener backwash water have no deleterious effect on the biological function occurring in the septic tank and may, in some cases, be helpful.
b) The additional volume of wastewater generated is added slowly to the wastewater stream, and does not cause any hydraulic overload problems.
c) Soil structure in the soil absorption field is positively affected by the calcium and magnesium ions in water softener effluent.
Based on a detailed evaluation of information and studies performed in this area to date, we conclude that water softener regeneration discharge does not negatively impact common on-site aerobic septic systems. Slightly elevated levels of sodium in regeneration discharge do not seem to effect septic system microorganisms, and may indeed benefit the septic process.
Other matters seem to play a much more important role in proper septic tank function. You should always minimize the amount of household cleaners that enter the waste stream. Whenever possible, reduce the use of soap and harsh chemical cleaners, and consider “natural” products containing low levels of phosphates. If you already have a water softener installed, remember that you can reduce the amount of soap use substantially – by as much as 50% to 75% – soap no longer has to work as hard to remove the minerals already removed by a water softener. Avoid using a garbage disposal with an on-site septic, as minimizing these types of organic wastes will reduce the load on the system. And finally, reduce when possible the amount of water flowing into the system from showers, baths, washing machines and dishwashers.
Work in this area is on-going, and a symposium discussing this issue is scheduled for March, 2006 in Chicago. A joint task force has been established between the Water Quality Association (WQA) and the National Onsite Waste Recycling Association (NOWRA) to plan and oversee joint activities and investigate any future findings. Failures of specific on-site septic systems will also be examined by this task force in order to determine the cause.