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How Do Water Softeners Affect Septic Systems? 

By: Craig Smith
Published on:
How Do Water Softeners Affect Septic Systems

Those that have a home with a septic system and have a water softener on their incoming water line (or are thinking about getting one), may be wondering if that softener has any impact on their septic system. 

It’s a great question as septic systems need to operate in a balanced way for them to be effective. 

Homeowners also do not want to overburden these systems with high amounts of wastewater routinely going into them such as softeners sometimes create. This article will answer the question ‘can a water softener and septic system coexist’.  

How Water Softeners Work 

First off, it’s important to note that this article will only focus on salt-based water softening systems.

That’s because salt-free water softeners only ‘condition’ hard water minerals as opposed to removing them, so no salt is used in the process. They also do not create any other potentially harmful conditions that affect a home’s wastewater that is discharged into a septic system. Quite the opposite is true for salt-based water softeners, and that will become clear as how salt-based water softeners work is described next.

Also note: For the rest of this article the term ‘water softener’ will refer to a salt-based water softening system.


As someone looks at these somewhat large, dual-tank water treatment systems with digital control heads, it’s easy to assume that they work based on a complicated process. That is far from the truth. They work utilizing a very simple ion exchange process.

The main tank (the taller and thinner ‘resin tank’ pictured above) contains special resin beads. These resin beads get coated with a salt mixture that comes from the brine tank (the shorter and wider tank pictured in the photo above). The positive sodium ions in the salt mixture attract to the resin beads and stick to them.

As the water in the incoming water line passes through the resin tank, it contains hard water minerals such as calcium and magnesium. These have much stronger positive ions than that of the sodium ions that are coating the resin beads. These hard water mineral ions then are ‘exchanged’ with the sodium ions and now stick to the resin beads. This eliminates the hard water minerals in the incoming water and later they will be flushed out of the system during a wastewater-causing regeneration (backwash) cycle. 

This process also puts a small amount of salt into a home’s tap water and that additional salt will eventually end up in the wastewater in a septic tank. It’s this increased salt content added to a home’s water because of the ion-exchange process water softeners use that concerns some that use a water softener with septic system.

How Septic Systems Work


A septic system is another large setup that seems like it would involve a complicated process but doesn’t. 

Three main components make up a septic system. These are the septic tank (can be made of concrete or thick, rigid plastic) , a distribution box, and a leach field or drain field.

Wastewater first flows into the septic tank. Here solid deposits in waste known as sludge sink to the bottom and lighter material form a scum layer near the top of the tank. Both the top and bottom layers decompose over time with the help of bacteria that naturally occurs in human waste. Excess water is let out into the leach field by a port on a septic that is located just under where the scum layer would form. That way none of that scum layer ends up in a leach field.

The Potential Negative Effects of Water Softeners on Septic System

There were some studies done on septic systems that had water-softener wastewater flowing into them as far back as the 70s. These were done because many started to think there was a correlation between an increase in septic system failures and the rise in the popularity of water softeners that use salt. 

Many of these studies were inconclusive or showed that a water softener had little or no impact on a septic system.

But a newer study done by the Water Quality Association (WQA) in conjunction with the Water Quality Research Foundation (WQRF) suggested that water softeners do make an impact on septic systems. 

Excess sodium that’s generated when using water softeners and eventually ends up in septic tanks can slow down the bacteria degradation rate. This, in turn, can decrease the efficiency of a septic system. Increased salt levels in a septic tank are also thought to raise PH levels which can harm essential bacteria. Some schools of thought suggest excess salt in wastewater can also cause concrete septic tanks to break down faster.  

The figures generated in the above-mentioned study, although they did not appear to be hugely significant, are still worth noting.

How to Use a Water Softener Safely with a Septic Tank (Solutions)

The answer here is a simple one. Based on the information that’s been presented so far in this article, it’s ok to use a water softener septic system combination in most cases with just one hitch. 

The homeowner should choose the best water softener possible. That’s a modern water softener model that is both salt and water efficient and only regenerates when its sophisticated controls tell the system it’s necessary. That should result in lower salt levels in the wastewater inside one’s septic tank.

A homeowner can also opt for a salt free water softener to eliminate this potential problem completely if they have moderately to slightly hard water.

Using potassium chloride as opposed to sodium chloride in a softener system may also help. That’s because potassium chloride is thought to be less disruptive to septic tank bacteria since it does not raise the PH of water as high as sodium chloride does. The higher the PH level in water, the harder it is for bacteria to survive.  


What has been detailed in this article should be of some concern to homeowners that have a septic system in their yard and a water softener on their incoming water line. 

The question is how much of a concern should it be? 

According to the information presented here, it should only be of slight concern. Especially if one’s septic system seems to be performing well and does not require excessive maintenance to keep it that way. Just to be safe, it’s suggested that using a modern, more efficient water softener model or a salt-free softener will even further reduce the chances of one of these popular water treatment devices impacting one’s septic system. 

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Craig Smith
Craig got his start in water working in the swimming pool and spa industry. Water treatment would grow into his main career but he ended up working in the pool industry for over 26 years where much of his time was spent balancing the water in customer's swimming pools and installing water filtration equipment. Craig offers an abundance of water treatment knowledge after helping homeowners get pure water for 26 years.

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