Draining a water softener into a septic system...bad idea?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Mikebarone, Oct 3, 2008.

  1. Mikebarone

    Mikebarone DIY Senior Member

    Phoenix, AZ
    I have a client that the water softener discharge line drains into her sewer line that goes into her septic system. I noticed on my dads discharge line on his water softener, (that he just discharges on the ground) that it, (over time) leaves a crusty salt layer on the ground.
    On my clients house, will the salt get into her leach field area, (under ground) and leave that same crusty salt layer, and, (in time) reduce the life of the leach field and even kill some of the good bacteria in the septic tank?


  2. nhmaster

    nhmaster Master Plumber

    S. Maine
    Very bad idea indeed. Yes the salt kills the bacteria both in the tank and the leachfield.
  3. Redwood

    Redwood Master Plumber

    It depends on who you talk to!

    In my state it is prohibited as the claim is made that it does what NH Master claims...

    Other places it is fine and claimed to actually be beneficial...water-softeners/effects-of-water-softener-discharge-on-septic-systems

    The work I do is done in accordance with the laws of my state.

    I will say though That I keep a rather large freshwater aquarium That relies heavily on a biological filter. I.E. fish poop in the gravel consumed by bacteria and one of the things I do to maintain a healthy aquarium is add Aquarium Salt to the water.
    Last edited: Oct 4, 2008
  4. Gary Slusser

    Gary Slusser That's all folks!

    The oceans are full of bacteria and have very salty water, much saltier than the diluted discharge from a softener that is then further diluted in at least normally, a 1000 gal septic tank, and in many cases a larger than 1000 gal tank.

    Millions of softeners discharge into a septic tank without problems and have been doing it for many decades.

    The EPA has done two studies over the last 20-30 years and the results of the first study caused a number of the very few States with bans on the discharge to lift them. There are only about 3-5 that have bans.

    The EPA says that there is no negative change in the operation of the septic system and if any change at all, it's a slight improvement due to the additional water.

    In the vast majority of locations, it is illegal to put the discharge on or in the ground because it contaminates soil and groundwater.

    IMO it belongs in the septic system.
  5. jimbo

    jimbo Plumber

    San Diego
    California is coming close to banning softeners alltogether. I keep hearing it has to do with salt. Maybe with the wasted water. Who knows!
  6. Redwood

    Redwood Master Plumber

    Or maybe the Culligan Man is stuffing The Terminator's back pocket...:cool:
  7. Gary Slusser

    Gary Slusser That's all folks!

    The CA governor vetoed that bill. The problem is chloride content in sewage treatment plants. The cause is the high chloride Colorado River water and irrigation but softeners were being blamed.
  8. 99k

    99k Radon Contractor and Water Treatment

    Fairfield Co.,Connecticut
    As Redwood noted, our state doesn't allow backwash in the septic. So the best solution is to direct it in a downspout drainage pipe (if available). The problem with just dumping it on the ground is that the salt can damage/kill vegetation.
  9. Mikebarone

    Mikebarone DIY Senior Member

    Phoenix, AZ

    Thanks everyone for all the feed back!

    I'm in Phoenix AZ and as far as I know the city / state haven’t addressed the issue of banning the discharge of water softeners into the city sewer systems….yet.
    After reading all of the replies to my question, I guess I can leave that sleeping dog alone, and go back to getting her A/C duct working properly….LOL.

    Thanks again,

  10. leejosepho

    leejosepho DIY scratch-pad engineer

    My softener's backwash went into my septic tank until just a few days ago, and I expect to see a significant difference in my tank over the next few months. The tank in question is only a 500-gallon tank, but the softener backwash and two toilets were all that were dumping into it ... and after only about two years, my outlet filter had to be cleaned weekly.

    Since having the tank cleaned and pumped last week, the owner of the septic company that serviced my tank has told me about a demonstration he observed at a County Heath Department. An aquarium had been set up to represent a septic tank with sludge in the bottom, then salt water was introduced. Accdording to what I have been told, the salt water settled at the bottom of the tank and floated the sludge that was then stirred around by a normal flow of effluent coming into the tank.

    My softener's backwash now goes into a small drain field of its own.
  11. Gary Slusser

    Gary Slusser That's all folks!

    All softeners have a DLFC (drain line flow control) it controls/limits the max gpm flow to drain. The max gpm DLFC for a large residential softener would not be more than 5 gpm. Most won't flow more than 2.7 gpm. A backwashed or regenerated filter can go to 10 gpm.

    The vast majority of residential softeners have a 1/2" ID drain line. The 100% saturated brine from the salt tank is diluted down to 8-13% brine as it is drawn from the salt tank and mixed with the water in the resin tank before it exits the softener's drain line.

    The flow from a 1/2" ID drain line going into a house drain and then into the main sewer line into a septic tank is not going to stir up sediment or anything else in a 500 gal or larger septic tank.

    A fish tank model is not a septic tank...

    I think you aren't using enough water to keep your 500 gal system operating correctly. What is the minimum gpm flow rate of those filters? I have had two 500 gal tanks with a single leach bed line from each, with 1 for a full bath, and the other for a half bath and kitchen sink that were pumped three times in 56 years with 2-5 people living there. Those tanks didn't have any filter on the outlet or in the leach lines; that filter thing sounds like a money maker to me. There was no softener or filter draining into either.
  12. leejosepho

    leejosepho DIY scratch-pad engineer

    Sure, and I believe the flow in the demonstration was representative of the discharge from a washing machine or bath tub.

    After being pumped, it only took five days for the 500-gallon tank to fill. The problem I had was the presence of suspended solids not breaking down or settling on the bottom.

    I do not know, but they only restrict flow when they are clogged with particles.

    With my own softener now out of the picture, I hope to achieve the same!
  13. Gary Slusser

    Gary Slusser That's all folks!

    With your softener's discharge water now going into a drain field of its own you are polluting the ground water; that's illegal in many more States than the number of States with a ban on using the septic tank. And you've done this after watching a fish tank model demonstration...

    You said you had two toilets and the softener discharge going into the 500 gal tank. Now you mention a washing machine and a sink stirring up the sludge... you didn't have either and I don't think a toilet or two would stir up sludge so it gets out of the tank but if it did, it proves your tank baffle isn't doing its job.

    I say that any filter in a septic system drain field line will reduce flow from the first drop of water that's run through it; even brand new it's a restriction in flow that's designed to have an ever increasing restriction to flow. A money maker fer sure for those selling that type of septic system.
  14. leejosepho

    leejosepho DIY scratch-pad engineer

    I did not see the demonstration -- a licensed septic installer told me about it after he had seen it, and he has also told me the drain field I now have for the softener is fine. However, I do understand the issue of dilution, and I will definitely check into that. If necessary, I will come up with some kind of system to add water to the flow at the time of backwash discharge.

    The baffle is fine and doing just as it should -- it cannot stop sediment from coming up off the bottom for whatever reason. However, I do believe my outlet drop pipe was too close to the bottom of the tank ... and I have since shortened it. It was a couple of inches below the baffle. Overall, though, my suspicion is that a bag of salt per week going into that tank was at least contributing to whatever was causing visible solids to clog my filter, and now we will see over the next few months.

    The filter I use is designed to keep solids out of my drain field, and not to restrict flow. It is actually a very simple filter that looks like a large bottle brush, it is inexpensive, it last "forever" and it is very easy to rinse clean:

  15. Cobra1365

    Cobra1365 New Member

    My system used to drain into our septic. When it destroyed my distribution box (concrete) I re-routed it to a french drain system. Over time, the salt will eat away a concrete system.
  16. leejosepho

    leejosepho DIY scratch-pad engineer

    Yesterday I saw a documentary showing how that helped make escape from Alcatraz a bit easier! In a labratory test, the concrete failed at about 850 PSI (rather than the typical 5000 PSI), and the guy in the lab could further crumble the broken pieces with his fingers. Also, there are buildings in Key West that are now crumbling (and have been for many years) because their concrete was made with aggregate that came out of the ocean.
    Last edited: Jun 9, 2013
  17. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    My softener discharged into my septic for 15 years in the last house and 13 so far at this one with no problems. And since there are many softeners in the Phoenix Metropolitan area and most, if not all, discharge into the city sewer or septic systems, I doubt that it is a major problem.
  18. craigpump

    craigpump Well-Known Member

    The state of Ct is working on legislation that will ban backwashing into septics. The state wants there to a dry well for the systems to backwash into, some towns are being proactive and have their own requirements for dry wells already.

    According to the few guys I know who do septic work, the salts are destroying the d boxes and tanks.
  19. WorthFlorida

    WorthFlorida USCG escorting cruise ship leaving Port Everglades

    Lake Worth, Florida
    I wish someone from a water softener manufacture could answer this but some good info is at

    It reads,

    Regeneration of ion exchange resins
    When all the available Na+ ions have been replaced by calcium or magnesium ions, the resin must be re-charged by eluting the Ca2+ and Mg2+ ions using a solution of sodium chloride or sodium hydroxide depending on the type of resin used. For anionic resins, regeneration typically uses a solution of sodium hydroxide (lye) or potassium hydroxide. The waste waters eluted from the ion exchange column containing the unwanted calcium and magnesium salts are typically discharged to the sewage system.

    It is not typical salt that is used in the softener that is discharged, but don't worry when it snows, millions of tons of salt are dumped on the roads that all wash away to the rivers and streams.
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