Water Softener and Septic Systems: How to Ensure Compatibility

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If you have a private septic system on your property, you might be wondering whether a water softener might affect the septic tank – and how you can best ensure compatibility between the two systems.

We’ve shared everything you need to know about water softeners and septic systems in this guide.

📌 Key Takeaways:

  • Some sources say that sodium chloride in water softener brine may affect the performance of bacteria in septic systems and lower the hydraulic conductivity in the drain field.
  • However, other studies have found that the salt in water softener brine might actually be good for anaerobic digestion in a septic tank.
  • To ensure compatibility between a water softener and a septic system, buy an efficient water softener, make amendments to your septic system design, and consider swapping sodium for potassium in the brine tank.

🔎 Water Softeners: A Quick Overview

A water softening system is a type of whole-home water treatment appliance that tackles the common issue of limescale.

By removing the minerals responsible for water hardness, a water softener prevents the effects of hard water, including scale formation on pipes and appliances. This helps to maintain good water flow and appliance efficiency.

Water softeners use a softening process known as ion exchange to replace calcium and magnesium ions with sodium ions (salt). Every few days, water softeners regenerate, flushing the resin beads with salt brine to remove the accumulated hardness minerals and replenish the sodium.

Water filtration and softening systems next to water heater

🔎 Septic Systems: A Quick Overview

A septic system is a buried underground container that consists of a drain field, a septic tank, and a distribution box.

A septic system is connected via pipes to your home, allowing wastewater to travel into the septic tank, where the heavy solids and the lighter materials separate.

Gradually, the waste in the septic system decomposes, helped along by naturally occurring aerobic and anaerobic bacteria. Water is discharged from the septic tank into the drain field.

Septic drain field system

🤔 Are Water Softeners Harmful To Septic Tanks?

So, now we know how a septic system works and why people use water softeners, is there a danger of these systems combined?

If you’ve already done some research into the effects of water softeners on septic systems, you might be feeling fairly confused. That’s because the information on this subject is conflicting.

Some sources say that water softeners are bad for septic tanks – and, in fact, some states restrict the use of water softeners due to this reason (amongst others).

However, a study was conducted in the 1970s by the National Sanitation Foundation (NSF) that concluded that water softeners had no detrimental effects on septic systems. Both the Environmental Protection Agency (EPA) and the Water Quality Association (WQA) endorsed this study and agreed that there are no effects of water softeners on septic systems.

🧐 Why Might Water Softeners Harm Septic Tanks?

The theorized reason why water softeners might harm septic tanks is that the backwash during the regeneration process may compromise the good bacteria in a septic tank, which is needed to break down the waste.

All water softener systems need to regenerate as part of the water softening process. Regeneration is when the water softener flushes the resin tank with a salty solution called brine, to lift the accumulated hardness minerals and replenish the resin beads with sodium ions.

Once this salty water has been used to flush the resin, it’s sent down a drain, where (in homes with septic systems) it ends up in the septic tank. Some sources say that the high salt content of the brine solution may reduce the rate of sewage breakdown in a septic tank because of its effects on the naturally occurring bacteria.

The brine discharge may also reduce the space in the septic tank that could be used to store the solid waste, resulting in the need for more frequent emptying.

We should also consider what happens when the brine solution is sent into the soil absorption field. There’s a theory that the sodium chloride in the solution could cause the underlying soil to become damaged, but the actual evidence to support this theory is largely inconclusive.

Water softener backwash rinse override

📋 How Might Water Softeners Have A Positive Influence On Septic Systems?

You’re probably feeling nervous about using a water softener with a septic system by now.

However, there is evidence on the contrary to suggest that water softeners aren’t only not damaging to septic systems, but that they might even benefit septic systems.

For instance, a study conducted by the University of Wisconsin looked at what might happen if a water softener is installed before a septic system and found that actually, the sodium chloride in the brine might optimize the organic waste treatment process by aiding the growth of aerobic bacteria.

So, it’s clear that more studies are needed to establish the link between a water softener and a septic system and confirm for certain whether the brine discharge from a softening system is good or bad for waste breakdown.

📖 How To Ensure Compatibility Between Water Softeners And Septic Tank Systems

Here are the best ways to make sure your water softener is compatible with your septic system.

Buy A High-Efficiency Water Softener

Our top recommended way to ensure compatibility between a water softener and a septic system is to buy a high-efficiency water softener.

Efficient water softeners will only waste the necessary amount of salt water, while an inefficient system may regenerate too frequently or waste a high volume of brine, resulting in too much salt and water leaving the tank.

We recommend a water softener that performs demand-initiated regeneration, which means it calculates when it needs to regenerate based on your water hardness and daily water usage. So, he softener will only regenerate when it needs to, rather than regenerating to a set schedule, which could result in excess brine discharge.

The most efficient water softeners use Water Efficient Technology, meaning that they only use the required amount of salt and water in the water treatment process.

Here are the best water softeners for septic systems in 2024, selected by our experts.

Use Potassium In Your Softener

If you’re still uncertain about using a water softener because your home has a septic system, switch to potassium chloride in the brine tank.

Potassium chloride plays the same role in the ion exchange process and is just as effective as sodium chloride (salt) at producing softened water. But there are no concerns about the effect of potassium chloride on septic tank bacteria, so it’s a good alternative to salt for folks with concerns.

Morton Potassium Chloride Pellets

Alter The Design Of Your Septic System

If you’re in the process of designing a septic system, make sure it’s suitably designed for use with a water softener.

First, size up. Your septic tank will need to have a large enough capacity for your waste and the additional hydraulic load from the softener.

Also, if you can, don’t use clay in your drain field. You’re more likely to have issues with clay soils because of their low hydraulic conductivity. At least try to avoid swelling clay in the leach field, which will go some way to reducing the effects of the high sodium concentration in the field.

📑 Alternative Option: Buy A Salt-Free Water Softener

Alternatively, if you’re concerned about the effects of a water softener on a septic system or you live in a state that restricts the use of water softeners in such situations, consider buying a salt-free water softener.

Salt-free softeners use a conditioning process that alters the formation of hardness minerals, preventing them from forming scale. They’re known as conditioners or descalers because they don’t produce softened water – water is technically still “hard” because it still contains hardness minerals.

A water conditioner doesn’t use a brine tank and doesn’t need salt to operate. It also doesn’t regenerate or release sodium chloride in wastewater, so it’s a good option for folks who would rather avoid these effects of water softeners altogether.

  • Brian Campbell
    President & CEO, CWS, CWR

    Brian Campbell, a WQA Certified Water Specialist (CWS) and Certified Water Treatment Representative (CWR) with 5+ years of experience, helps homeowners navigate the world of water treatment. After honing his skills at Hach Company, he founded his business to empower homeowners with the knowledge and tools to achieve safe, healthy water. Brian's tested countless devices, from simple pitchers to complex systems, helping his readers find the perfect fit for their unique needs.

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