My wife and I moved into a home that had been rented for a while. Looks like lots of maintenance has been deferred to us, including the water softening system.

We noticed some mold in the tank during inspection. The inspector did not seem too concerned with it. Is this something that will be harmful if left untreated? How aggressive should I be getting about cleaning the tank? Will household cleaning solution (e.g. bleach) be worse for us than the mold if it enters the tank?

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    No knowledge of these tanks, so just a comment: Household chlorine bleach, as long as it is just bleach and not scented or with other additives, is exactly what you use to disinfect water. It is used by many municipal water systems as well as (at a higher level but for swimming not drinking) swimming pools everywhere. In fact, many bleach bottles will even tell you how much (it normally doesn't take much) bleach to add to water to safely disinfect (enough to kill the bad stuff but not enough to hurt people drinking it). May 10, 2020 at 16:03
  • Personally, I would bleach to crap out of it and not use the water for a day and then run a tap until the bleach smell is gone. Probably like a half gallon of non-concentrated bleach and fill it with water May 10, 2020 at 17:42
  • That just looks like normal crud from buying less than perfect salt. What makes you think it’s mold? May 10, 2020 at 23:18
  • @Harper-ReinstateMonica Good question. It has a musty smell that I attribute with mold. I guess I could try to scrape some out to get a better look at it.
    – Yuck
    May 10, 2020 at 23:23
  • @UnhandledExcepSean "bleach to crap out of it" Crapping out of your water softener tank is probably worse then mold.
    – Alaska Man
    Mar 7, 2021 at 20:08

1 Answer 1


This is the salt water brine tank that is used to let salt set in the water to make brine which is then flushed through the resin in the softener before being rinsed to the drain. So a bunch of things are good to keep in mind as this is not a hazard. Most molds, especially those which form in water are not hazardous, only a few which we might breathe the spores. This is not what you drink directly but only what is used to reset the ion exchange. Salt is, in itself, used to delay bacteria, as in treating meats like ham or salt pork. The chlorine in the water used to make the brine will kill most harmful bacteria as it does in the normal water treatment.

I would suggest cleaning as a way to make it "feel" better, even though it is mostly just dirt, possibly from using less clean salt like perhaps blocks of stock salt. Then the barrel should be topped off with salt to allow it to make brine as at the current level, the softener is not going to have enough brine to operate. To avoid doing it more often, I like to nearly fill the barrel.

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