An 18-month research project has found that water softeners, when operated efficiently, do not harm septic systems or affect their ability to properly treat wastewater. The question has been raised for decades despite other studies that have had the same result. 

“If a water softener is set at an efficient salt setting, the impact on septic systems is very limited if any at all,” says Pauli Undesser, director of regulatory and technical affairs for the Water Quality Association and foundation coordinator for the Water Quality Research Foundation, which funded the study. It was conducted by John Novak, Ph.D., P.E., through the Virginia Polytechnic Institute and State University with a steering committee consisting of the Water Quality Association, NOWRA, and NSF International, a global standards-setting organization. 

According to the study’s executive summary, water softeners operating at or above about 3,000 grains per pound of salt efficiency can actually improve septic tank performance. Those operating at or below about 1,000 grains per pound may have a negative effect. Those cases, Undesser says, are limited and can be addressed by adjusting water softeners to use less salt or replacing them with better technology. 

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There are signs an onsite professional can be aware of that indicate a sodium/calcium imbalance from a water softener may be causing problems. “If the separation isn’t happening — the sludge settling out and the FOG coming to the top — it could be an indication,” Undesser says. The so-called “milkshake effect” can also be caused by other issues. “They can look at having the settings adjusted to make it more efficient.” 

The results of the study did come out as expected. “We hear a lot of talk about water softeners always being a problem, and that’s not the case,” she adds. “It’s really a dialogue we’d like to have between the two industries to make sure consumers are doing a better job of keeping their softeners at efficient levels, and how the onsite industry can work with water treatment professionals to make sure consumers are doing the right thing for the health of the septic system.” 

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Conducted from May 2011 to the summer of 2012, part of the research was done in the lab with real septic waste to allow for many more samples and comparisons in a short amount of time. “Novak also did real-world testing at a retirement home that was divided so he could look at three different septic systems from one facility,” Undesser says. “He looked at different levels of salt and regenerant going into each of those to come up with the final conclusions.” 

Perhaps the results from this research aren’t groundbreaking, but the new study continues the ongoing discussion among industry experts on the effects of water softeners and regeneration water on onsite systems.

Four years ago, pumpers and onsite professionals responded to a COLE Publishing forum survey from NAWT Secretary Tom Ferrero, asking about conditions they saw in septic tanks and absorption areas that they attributed to water softeners. The attribution was based on the problem going away once the water softener was disconnected from the onsite system. 

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The survey was prompted by a workshop that included members of the Water Quality Association, Water Environment Research Foundation and the U.S. EPA that were tasked with determining whether further research was necessary to understand the effect softened water and regenerated water from water softeners may have on onsite systems. NAWT was asked to provide the pumpers’ perspective, so Ferrero wanted to find out what that was from our readers. 

The 30 responses received fell into five categories, listed in order of frequency: 

1. Hydraulic overloading from the backwash cycle or water softener leaking. Most leaks average 200 gpd, but we once clocked one at 700 gpd, and we couldn’t notice or hear it. 

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2. Disruption of settling in the septic tank. The argument is that salt water is denser than water, allowing more solids to prematurely clog the effluent filter and float out of the tank. However, a presentation on “Monovalent & Divalent Cations and Their Effect on Settling” by John T. Novak, Ph.D., P.E., Virginia Tech, explained the relationship that sodium, calcium and chloride ions have on settling. The sodium ion has a single or monovalent charge and the calcium ion has a double or divalent charge. When the ratio of monovalent charges to divalent charges is imbalanced, it effects settling. Novak conducted his research at wastewater treatment plants, but the basics are identical. 

3. Chemical and biological upsets such as no scum layer or a scum layer that looks like and has the consistency of milkshakes with no stratification in the septic tank. Scientists in the group confirmed that salts can emulsify grease, keeping it suspended in the tank and, therefore, able to reach the drainfield in the effluent. 

4. Structural deterioration of distribution boxes and concrete baffles. Presentations revealed that sodium could increase the production of sulfides and hydrogen sulfide, which reacts with oxygen to form sulphuric acid. It is sulphuric acid that erodes the concrete in the upper reaches of the tanks and d-boxes. 

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5. Clogging of the soils or peat and sand filters, which is logical if more grease and solids are leaving the tank. 

Bottom line? Scientific explanations corroborated anecdotal evidence pumpers and onsite professionals saw in septic tanks and absorption areas that they attributed to water softeners. 

The new study is being prepared for publication. Undesser adds that WQA would like to hear from onsite professionals who may have personal experience that doesn’t match up with the study results. “If there are issues they are seeing, we’d like to hear more about it. If they feel the research isn’t adequately showing reality, we’d like to know that.”


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