Photo of a home water softener systemWater Softener Salt Effects on Drinking Water, Plumbing Systems, Heating Equipment & Septic Systems

  • SALT / SOFT WATER IMPACT on SEPTIC, PLUMBING, HEATERS - CONTENTS: an explanation of the impact of water softener salt on drinking water, the plumbing system pipes, heating equipment, and on the septic tank and leachfield or soakpit. Will the Water Softener Salt or Water Volume Damage the Septic System?Water hardness or softness - mineral level - effects on heating equipment, plumbing systems, boilers, water heaters, piping & tankless coils
  • POST a QUESTION or READ FAQs about the effects of water softener or water conditioner salt on drinking water & on septic system life

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Water Softener Salt Effects on Drinking Water & on Septic Systems - water softener salt problems:

This article explains the effects (and potential damage or harm) of water softeners on septic systems.

Some septic system experts assert that salt discharged into the leach field is an important factor in shortening the life of the biomat which forms below the leach field (to treat effluent as part of the sanitizing process for septic effluent).

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Photo of water softener interior showing saltSalt or Water Loading of the Septic System: Will the Water Softener Salt or Water Volume Damage the Septic System?

Certainly high levels of salt can kill septic tank or drainfield bacteria.

But a normally-operating water softener is unlikely to harm the septic system.

We start by agreeing that a malfunctioning water softener may damage a septic system in two ways:

  1. Water volume in Septic Fields from Water Softeners: The normal water softener backwash cycle is less than 100 gallons and is not a major source of daily water usage at a property (see "Determining Needed Septic Capacity" at "More Reading" below).

    If the timer or valve gets stuck in the "backwash-on" cycle (which I have seen happen), the system will run continuously and will flood the septic leach field. This is discussed in "Clogged Drain Diagnosis" referenced at "More Reading" below.

  2. Salt dose of Sodium and Chloride in Groundwater from Water Softeners: Part of the water softener backwash water contains no extra salt. During an interval of backwash however, some water may be quite salty, perhaps 5,000 ppm to 10,000 ppm.

    If the salt dose (which is also adjustable on many water softeners) is set incorrectly high excessive salt may be discharged into the septic system where it may damage the leach field and its biomat.We encountered this condition at a property where the owner had first set the salt dose to the maximum and then set the backwash frequency to a maximum as well, when neither was needed for the level of hardness of the water.

    A Michigan DES study of community wastewater treatment systems (not private septic systems) reported that sodium and chloride in the soil at their discharge sites greatly exceeded federal drinking water limits.

    This point needs more research since it's not clear that groundwater is required to meet drinking water standards - this is a shortcoming of the Michigan article.

    The article continued to cite 120 m/l for sodium and 250 m/l for chloride as the maximum allowable levels in groundwater. (See "Sodium and Chloride and Water Softeners" at "More Reading".)

  3. Water softener salt at normal levels will not kill septic tank bacteria

Closeup photo of water softener salt in the handNormally the water softener salt and chloride should not be a problem for the septic system: One of my clients is a biochemist who specializes in studying septic bacteria.

His opinion was that in a normally-working home water softener system the level of water softener-produced salt in the septic tank was so diluted by other water flowing into the tank that in his experience it never reached a level that was harmful to septic tank bacteria.

We are not sure if this same conclusion applies to bacteria in the drainfield biomat. Gayman and others have conducted research on salts in drainfield soils and their role in drainfield life.

More details about salt in wastewater are at WASTEWATER BIOCOMPATIBILITY.

Normally water softener water volume should not be a problem for the septic system.

See REDUCE IMPACT of SOFTENER on SEPTIC and then be sure to read

SOFTENER ADJUSTMENT & CONTROLS to be sure that your water softener is operating properly.

Water Softener Maintenance Tip: Should You Use Potassium Chloride (KCL) ?

Some water softener manufacturers such as for the Sears Kenmore electronic water softener recommend using potassium chloride "salt" (KCL) instead of standard sodium chloride (NaCL) which is standard or ordinary salt. and remark that potassium chloride salt will give longer equipment life and will permit lower hardness settings on the water softener control.

Kenmore explains that if you are not using KCL in their water softener you might need to increase the equipment's hardness settings by 25%:

If your softener does not have a KCl salt setting, you must increase your hardness setting by 25% to ensure continuous soft water.[21]

Watch out: Sears-Kenmore warns:

A softener using KCl should not be placed in areas with temperature fluctuations and high humidity (KCl will harden in these environments and may make the softener inoperable.

Check the brine tank and brinewell (black tube in salt storage tank) monthly. If hardening is present, pour small amounts of warm water onto hardened areas until they loosen. [21] 

If your water softener does not have a KCl (potassium chloride) salt setting you must incrrease your hardness setting by 25% to ensure continuous soft water.

Reader Question: slimy scum water softener problems along with septic system failure - due to water softener?

Since I installed my water softner, I've noticed a few changes.

The first was a slimy scum that had formed in my main line water filter. Upon further investigation, this scum was also forming inside the toilet tanks.

The second thing that I noticed was a break-down of my septic system. I have a double septic tank that was pumped out a year and a half ago. I went five years without having to pump it since there is only my wife and myself at home. There is now a puddle of pungent water that keeps appearing over top of the septic tank.

These could be coincidental, but I think not since it was never a problem until the softner unit was installed. - Neil 4/11/12



I suggest following the procedures at SOFTENER CLEANING & SANITIZING, followed by a test of your water supply (ahead of the water softener) for contaminants. It also sounds as if you have two problems: unsanitary water in the home and a failing septic system.

A relationship between the water softener & septic could be that the softener's regen cycle is flooding the septic system tank & fields, but a puddle over the septic tank could be caused by other septic problems too. So also see SEPTIC SYSTEM INSPECT DIAGNOSE REPAIR.

For more depth of understanding of the possible issues, also see REDUCE IMPACT of SOFTENER on SEPTIC

Reader Question: does a water softener let salt water into the plumbing system?

Why does softner let salt water into lines - Anonymous 5/23/12

Reply: a review of water conditioners & salt effects


There are two "salt in water" topics when discussing as water softener or water conditioner: 1 = salt in the backwash or regen or recharge water run through the resin tank during a regen cycle and discharged into the sewer or septic tank, and 2 = salt that may be dissolved in to the building's water supply as that water passes through the water softener.

1. A water conditioner uses dissolved salt in water during the water softener regen cycle. A water conditioner or water softener works by exchanging sodium ions (salt) for magnesium or calcium ions that are dissolved in the water. It's magnesium and calcium at high levels in water that make it "hard" - high in mineral content. \

In order to recharge the resin tank in which the ion exchange process occurs, salty water is washed back through the tank - simultaneously moving calcium and magnesium out with the rinse water and recharging sodium ions in the resin tank. Because not all of the salt in the regen or recharge water stops in the resin tank, the remaining salt in the water being discharged exits into wherever the water softener backwash water is being drained.

2. A water softner will leave a small amount of dissolved salt or sodium in the building water supply as it passes through the water softener or water conditioner. If the conditioner is not properly adjusted the salt level in water could be excessive and can be both a health problem and a source of damage to septic systems.


But normally it's harmless. For people who need to be extra careful to eliminate all salt intake from their diet, some recommend installing a water supply line that can deliver water from ahead of or before the water softener, or installing equipment such as a reverse osmose system that will remove all salt and other minerals from just drinking water in the building.



Effects of Water Hardness or Softness on Plumbing & Heating Equipment, Heating Boilers, Water Heaters, Tankless Coils

Effects Hard Water (high in mineral content) on Building Piping, Water Heaters, Heating Boilers, Tankless Coils

The effects of water that is too high in mineral content are widely understood to lead to mineral deposits in building plumbing systems and heating equipment.

The percipitation of minerals out of hard water into or onto plumbing and heating components is generally more rapid and extreme at points of highest temperature in the system, but the effects of hard water on building mechanicals are also a function of the volume of water moving through the system. In sum, for hard water, the effects on building piping, heating equipment, water heaters, and tankless coils is a function of

  1. The hardness level of the water
  2. The volume of water that is run through the plumbing system, boiler, water heater, or tankless coil over time
  3. The temperatures of the water as it moves through the equipment
  4. The surface properties of the equipment. For example, using an acid flush to clean a tankless coil also leaves the coppe surface inside the coil etched and rougher than when new - possibly meaning that even with no change in the other parameters above, the time to clog-up again with minerals may be less than when the equipment was new.

Tankless coils used on heating boilers to product domestic hot water are particularly prone to clogging from minerals in hard water, as we discuss in detail atClogged Pipes / Tankless Coil De-Scale

Hydronic heating boilers themselves are less affected by hard water because except in the case of chronic leakage, the water placed into a hydronic heating boiler system is static - we are not normally constantly introducing new water and more minerals. However water chemistry is nevertheless important in some heating system applications, and special additives may be used to protect the system. Discuss this quesiton with your heating service company.

Steam boilers, unlike hydronic heating boilers, may indeed suffer from high mineral content in hard water, as new or makeup water is regularly requried and added (manually or by an automatic fill valve) in steam heating boiler systems. And as we just cited, water chemistry is nevertheless important in some heating system applications, and special additives may be used to protect the steam heating system.

Water heaters used to produce domestic hot water indeed suffer from scale formation from hard water. See WATER HEATER SCALE DE-LIMING PROCEDURE and WATER HEATER SCALE PREVENTION for details.

Effects of Soft Water (very low in mineral content) on Water Heaters & Heating Boilers

Lochinvar® LLC, a producer of high efficiency boilers, water heaters, and pool heaters, has produced an interesting technical bulletin that warns installers and building owners about special considerations when their equipment (and most likely that of other manufacturers when the heat exchanger is made of copper) is installed in buildings served by a water softener. [20] Quoting:

The required temperature rise and the standard pump used with Copper Heat Exchangers is based on the presumption of typical water chemistry of 8 – 25 grains of hardness, and less than 350 ppm dissolved solids (TDS). Caution must be used when heating water softened water below 8 grains. Typically commercial water softeners reduce hardness to 0 grains which may result in long term problems in the system.

When using softened water the installer must be aware that increasing temperatures causes an increase in the speed of chemical reactions. The rate of increase of chemical reactions approximately doubles for every 25 – 30 degrees Fahrenheit rise in temperature up to about 160 degrees F. The rate of water flow governs the rate at which the dissolved oxygen (essential to corrosion) is replenished at metal surfaces. Typically the corrosion is characterized by pitting resulting from metallic hydroxide and tuberculation reaction. Metal hydroxide dissolves the metal, and tuberculation reduces the hydraulic capacity of the tubing. Since this aggressive reaction typically happens at the metal to flow interface early heat exchanger failure can be expected.

Water heaters can be used in softened water but it is imperative that careful attention be paid to the heat exchanger. Proper operation will normally require setting the water heater with a lower flow rate and higher temperature rise.

Decreasing the flow rate will reduce the erosion process, however the heat exchanger should be monitored to ensure the scale/liming process is not exacerbated. The unit should be placed on a comprehensive inspection schedule until optimum flow rates can be established. Problematic water areas may require heat exchanger inspection every two weeks. The total scale accumulation should never exceed the thickness of a piece of paper. Should scale accumulation exceed this thickness the flow rate will need to be increased. The tubes should not have a bright shiny copper look. This would indicate that the erosion process has begun and the flow rate will need to be decreased. Once the proper flow rates have been established the inspection intervals can be increased to every 30 days, once a quarter, to a bi-annual inspection.

This procedure should insure proper operation of the unit as long the water quality stays consistent.
- Lochinvar, LLC World Headquarters, 300 Maddox Simpson Pkwy., Lebanon, TN 37090, Tel - Customer Service: 615-889-8900, contact Lochinvar Technical Service at 1-800-722-2101, Website: [20]

The company's technical bulletin includes a table that relates heater BTU Input Rates (between 90,000 & 500,000 BTUH), and Delta T at 0-7 grains of hardness compared with Delta T at 8-25 frains of hardness. We note that the higher the BTUH firing rate of the heating equipment, the higher is the required Delta T (temperature rise). For example,

  • a 90,000 BTUH input water heater [using a copper heat exchanger] handling water at 0-7 grains of hardness has its Delta "T" set to 8 degrees, while the same device handling water at 8-25 grains of hardness uses a Delta "T" of 5 degrees.
  • a 135,000 BTUH input water heater [using a copper heat exchanger] handling water at 0-7 grains of hardness has its Delta "T" set to 12 degrees, while the same device handling water at 8-25 grains of hardness uses a Delta "T" of 7 degrees.
  • a 500,000 BTUH input water heater [using a copper heat exchanger] handling water at 0-7 grains of hardness has its Delta "T" set to 40 degrees, while the same device handling water at 8-25 grains of hardness uses a Delta "T" of 28 degrees.

So you can see there is a significant change in temperature requirements for high-BTUH equipment.

Extensive quotation & technical review requested of Lochinar 12/15/12



Continue reading at REDUCE IMPACT of SOFTENER on SEPTIC or select a topic from the More Reading links shown below.

or see

SALT DOSE SETTING, WATER SOFTENER where we explain how to determine & set the water softener salt dose

OTHER SOFTENER METHODS examples of water treatment & water softening methods that do not use salt or ion-exchange.

HEALTH RISKS & WATER SOFTENERS possible health concerns for salt added to drinking water by a water softener.

Suggested citation for this web page

SALT / SOFT WATER IMPACT on SEPTIC, PLUMBING, HEATERS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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