Many homeowners rely on septic systems for onsite wastewater disposal. Those same homeowners often rely on cation-exchange water softeners to improve their water quality. The research indicates that when water softeners are operated properly and efficiently, they have no negative impact on septic systems and may improve performance. When a water softener is set very inefficiently or regeneration wastes are diverted, there could be negative consequences for a septic system.
By following the guidelines jointly developed and published by the National Onsite Wastewater Recycling Association (NOWRA) and the Water Quality Association (WQA), the wastewater discharge from the regeneration of household water softeners can be safely and economically discharged to onsite septic systems with no deleterious effect on the performance of the septic system or the environment.
A calculation tool is provided in the resource links on this page which will determine the expected monovalent to divalent cation ratio in a septic system, based on the influent water chemistry and the softener efficiency. Research has shown that this ratio is critically important. Water treatment professionals that install or maintain water softeners should use this tool to ensure that the predicted ratio is less than or equal to 5 if the softener regeneration discharge will be sent to a septic system.
And it is important to be aware of, and adhere to, any local codes and regulations regarding the discharge of water softeners.
Resources:
- WQA Position Paper on Water Softener Brine Disposal to Septic Systems
- WQA and NOWRA Guidance for the Use of Water Softening and Onsite Wastewater Systems on Individual Properties
- Water Quality Research Foundation (WQRF) Environmental Impact Study: Water Softener Effects on Septic System Performance – Executive Summary
- WQRF Environmental Impact Study: Changes in Septic Tank Effluent Due to Water Softener Use – Full Report (requires WQA membership)
- WQRF Softeners and Septic Performance Toolkit
- Potential Effects of Water Softener Use on Septic Tank Soil absorption On-site Wastewater Systems, The Effect of Home Water Softener Waste Regeneration Brines on Individual Aerobic Wastewater Treatment Plants – Combined Executive Summary
- Potential Effects of Water Softener Use on Septic Tank Soil absorption On-site Wastewater Systems, The Effect of Home Water Softener Waste Regeneration Brines on Individual Aerobic Wastewater Treatment Plants – Combined Full Reports
- Monovalent/Divalent (M/D) Cation Ratio Calculation Form)