Volume 44 Number 4
Water Softeners & Septic Tanks: A Compatible Combination?
Water Softeners Pose No Problems for Septic Tanks.” That was the headline of an executive summary published by the Water Quality Research Council (WQRC) in the late 1970s. The research was well-organized, independent and provided conclusive evidence to support the statement. No further research has been performed in the United States to challenge these findings; however, skepticism on the compatibility of water softener regeneration water with wastewater treatment system performance remains today. Much of this has originated from comments made by those that manufacture, install and service onsite wastewater treatment systems, based upon their field experience. This skepticism has led to a growing number of state and local sewage codes restricting softener use with onsite wastewater treatment systems.
These studies were designed to answer three questions:
Septic tank performance
The waste-consuming microbes can be negatively affected by various things. It’s common for manufacturers and installers of onsite wastewater treatment systems to educate homeowners on items appropriate for discharge, and those not to be discarded into the septic tank, such as cleaners, paints, cooking grease and oils, etc. In the case of water softeners, the question revolves around the impact on beneficial microorganisms by the added salt dosage from softener regeneration and, as a result, wastewater system performance.
The onsite wastewater treatment systems tested by NSF each received approximately 250 gallons of wastewater daily, seven days per week, as diverted from a municipal supply en route to a central treatment facility. One of the two systems received an additional waste stream from a water softener and was regenerated three times per day at approximately 3.5 pounds of salt/regeneration. The test was run for six months. Typical analyses were performed to determine proper wastewater treatment, including five-day biochemical oxygen demand and total suspended solids. No difference was detected in the treatment performance of the two systems over the course of six months.
In a water softener’s case, regeneration cycles of a typical three-bedroom home average 50 gallons per cycle of additional fluid contribution to the wastewater flow. With regeneration occurring generally every other day, average daily contribution is 25 gallons. Most tanks, as shown in Table 1, are sized a minimum of 50 percent larger than expected flow. At the low end of tank sizing, this is several hundred gallons of excess capacity. The softener contribution, therefore, is minimal and would have no expected impact on waste treatment system performance. This was confirmed in NSF testing of the two treatment systems discussed here.
Soil percolation rate
Water softeners contribute additional sodium and chloride ions to the absorption field. These have the potential to affect water flow through the dispersal field by swelling soil particles, thus reducing the average pore size. The University of Wisconsin-Madison researched this subject to determine impact on soil changes with softener regeneration water. They sampled septic tanks from 11 homes, five of which used water softeners. In support of their field analysis, researchers also investigated a number of theoretical conditions and other published research done on the same or similar issue.
Their findings concluded the softener regeneration water would create no adverse effect on the functioning of the absorption field.
Where are we today?
The most recent addition to the list is Texas, which implemented its new code restrictions on June 7, 2001. In light of these changes, recent meetings were held with NSF, WQA and representatives of the Texas National Resource Conservation Commission (TNRCC), who were responsible for writing and administering the Texas Onsite Sewage Facility Rules. These meetings underscored concerns of the TNRCC, representing the same issues intended to be addressed in the previous studies. Their confidence in the past research has been swayed by comments from the onsite wastewater treatment industry where field experience is apparently showing contrary results. To date, this hasn’t been quantified nor researched to determine if these findings conclusively show poor septic tank performance resulting from the softener regeneration water.
While it seems unusual that such information, neither researched or published, would lead to dramatic restrictions on water softener use, it’s important to understand the responsibilities of health officials. Local and state regulatory officials are charged with protecting public health and the environment. They’ll more often err on the side of conservatism for obvious reasons. It then becomes the responsibility of the industry, whether water quality or wastewater treatment, to challenge this conservatism with sound, credible research and data to alter such positions.
Further research may be of value and address a larger number of system types and field conditions. The expectation is that such research will only further prove the theory of the scientific community that addition of regeneration water, based upon salt concentration and flow, is simply too inconsequential to impact the performance of an onsite wastewater treatment system.
Until such time as more data are available that can be considered conclusive, it’s critical the water quality and wastewater treatment industries work in harmony with regulatory officials as new codes are developed at the local and state levels. Available research, field experience and comments should be presented for discussion and consideration prior to adoption of code language. This interaction will ensure code language is reflective of the best available information and takes into consideration all perspectives.
About the author
Table 1. Typical state code requirements for onsite wastewater treatment tank sizing*
*Based upon daily household waste stream flows (in gallons)
Table 2. States restricting softener discharge into onsite wastewater treatment systems**
** Massachusetts also restricts discharge to septic tanks for all water treatment devices, but the rule is not enforced currently.