This is a long, detailed post about my water problem. I've included all relevant info I can think of.

I bought my first house about 2 years ago, it's a ranch style with a finished basement and a pole building that has a finished area with a small apartment inside. In the last 2 or 3 months our cold water started smelling terribly of sulphur in the house, although not out of every faucet. There is no smell in the hot water, and we have never had this problem before.

We do have well water and our own septic tank. There is a water softener and a tankless water heater in the finished basement, where me & my boyfriend have our own living area. Most of the pipes in the basement are pvc. My mother lives with me and stays on the first level, where in her bedroom the previous owner installed a sink, shower & toilet. My mom has said her cold water in her bathroom sink has always had a slight sulphur smell, but aside from that one sink there was no smell in the house before recently. The smell seems to mostly be in the basement water and in my mom's room, I checked the kitchen sink & don't smell anything from the cold water there or in the other first level bathroom, which is weird. It doesn't make sense that our water would just start smelling badly out of nowhere, unless the previous homeowner was doing something to prevent this smell. I've done research and can't find any info on sulphur smell isolated only to the cold water. Everything I've read is either hot water or both hot & cold.

The only other issue we have had with the water is outside in the pole building apartment there is a standard hot water tank and the water will start to smell of sulphur & get stronger if we don't run the water out there for a few weeks. The previous homeowner said he adds a little bleach to the hot water tank out there whenever it starts to smell, then runs the hot water for a while to flush the tank the next day, and also completely drains the tank to clean it out every spring. I follow his instructions whenever the water starts to smell out there & that takes care of the problem. If I recall correctly it's the HOT water out there that smells.

Here is what we do & have done recently in the house:

-We change the water softener filter as recommended and flush the tankless water heater once a year with vinegar.

-We did change the filter out of a few months back and in doing so we checked the sink water to make sure it was off, when we did this the faucet shot out dirty water & air. After changing the filter we turned the sink back on and let it run for a few minutes to clear the pipes.

-We use the iron fighter salt pellets that the previous homeowner recommended for the water softener.

-This may be coincidence but we did run out of salt somewhere around the time the water started smelling and the softener tank sat empty for maybe a few weeks. Ever since then the water has not seemed soft when I shower, it feels grippy & dry instead of slippery & almost lotion like, even though it's been well over a month since we added the salt.

Anyone have any ideas on what would cause this and what I can do to eliminate the smell? Thanks in advance!

  • Does your hot water stink?
    – Kris
    Apr 14, 2021 at 18:02
  • Not at All, it's only the cold water Apr 15, 2021 at 19:50
  • Lots of comments and answers here, but let's face it, many situations are unique, it all depends upon the chemistry of the water, plumbing layout, what works for one person isn't going to work for another. I lived in my previous home for 20 years, served by a community water system that had the best water ever, no treatments ever needed by either the water company or individually. In my current home I have a high capacity well (great for irrigation), but terrible water quality. Very very hard water and Sulfides....required 2 types of treatment in series to make it usable. Apr 15, 2021 at 21:25

4 Answers 4


I have to somewhat disagree with Ed, which is rare. When a problem like the OP described that springs up suddenly, it's probably not a water quality issue. From wells, the water quality (or lack there of) is pretty consistent. What the OP is most likely to have is an anaerobic bacteria colony somewhere in the cold water plumbing. Sounds really nasty, but there is a fix. It's not uncommon, esp. when you have well water. I have had a similar experience at my home. You have to bleach the system. There are various methods to do this. Ed Beal described one. Others involve pumping / circulating a diluted bleach solution thru the cold water piping. The most important part is letting it sit for a few hours for treatment.

This is sort of gross, but just want to warn you that after treatment, and you turn the water back on to flush out the bleach, the cold could be VERY discolored. In my case I had a couple of faucets where the water came out BLACK! Totally black. Even after flushing for a long time, you may notice a slight chlorine taste for a few days. ....nothing to worry about, it will go away.

  • Thanks for the response George. The black water doesn't surprise me, when we turned the water off to change the water softener filter a few months ago it came out black for a minute when we turned it back on. Pretty gross. It makes sense that it could be in the pipes since we saw all that black water before. Especially because the water smells the worst in the basement, where it's closest to the pipes & water softener. I do have a water pump that we use to flush the tankless water heater, I'll look into flushing the pipes too. Apr 14, 2021 at 15:18
  • George, I somewhat agree but the op did mention running out of salt so untreated water got in the system, our system was so bad when we filled the pool or topped it off it was red. We could not drink the water in bypass at all. Bleaching is what my well guy (the one I have had do the well tests on property’s) recommends to kill the bacteria.
    – Ed Beal
    Apr 14, 2021 at 16:28
  • @EdBeal I missed the part about running out of salt, that would have let untreated water into the house. But I still think that they ended up with an anaerobic bacteria colony, maybe due to the softener running out of salt, but still...the main reason I say that is bc it's only in the cold lines. If it was due to the water source it would have affected the hot as well. The other clue is it's different in various parts of the house. Those bacterial colonies can be anywhere in the plumbing, I've had the same issue as the OP, some sinks were really bad, others with no noticeable odor. Apr 14, 2021 at 17:16
  • George, that makes sense to me. I've went around the house smelling all the sinks & it's only at the basement level & the sink in my mom's room. I'm going to start with the treatment and hope that clears it up. Apr 15, 2021 at 19:53

Short answer, very likely sulfate reducing ,or other bacteria are in the aquifer that your well water comes from. They generate hydrogen sulfide ; a person can smell much less than 1 ppm of H2S. These bacteria are even a problem in oil/gas wells as the H2S can increase corrosion.

I think one can find a small additive pump to add dilute bleach to the water entering the house; occasional small addition of bleach will stop the smell.

Or what a friend did is blow across the surface of a glass of water before drinking it, that removes the trace of H2S. Any heating, like cooking will remove the trace of H2S.


I have had a home that had horrible iron content and the water smelled of sulfur.

The water softener should take that out of the water.

Your mom noticed the sulfur in the past so she may be more sensitive to it. I would change the regeneration cycle on the water softener to a more frequent cycle.

Cycling more often will use more salt and water but it may be needed. Tho original owner may have had a lighter load on the system and the regeneration cycle was good for them.

Some machines cycle on number of gallons and some cycle on number of days. When you get the nasty water past the softener it takes time to flush them out.

The other thing you mentioned was when the water sits it is worse at the barn. This is really common with diaphragm pressure tanks bladder tanks don’t usually have as much air in contact with the water and that can create come bad taste /stuff on its own.

We used to bleach the well itself several times a year with standard Clorox bleach.

My well guy will use up to 3 gallons overnight then flush the well using an outside faucet that is not going through the softener for 2-3 hours.

It is a good idea to have the water tested, my area has water testing where for 10$ when they are running a special and 20$ normally. Take the water sample in and they check it and provide a report (if bad things in the well they suggest bleaching and sometimes adding UV systems to kill bacteria).

If you have ever had problems it is a good idea for regular testing and or bleaching of the well every year or 2 as needed.

In your case I might start with bleaching , let it sit in the well at least a few hours, overnight is better but don’t drink the water until the well has been flushed until you can not smell the chlorine.

  • Thanks for the response & tips Ed! I do have a contract with a septic company that deals with my specific type of tank, it's a Hoot Aerobic Tank system. They do testing once a year (its required where I live) and come out twice a year to maintenance it & change the filter. I need to give them a call as they are overdue to come out. Maybe that's what is causing the smell. Thanks again Apr 14, 2021 at 15:06

Your water softener may need cleaning.

I experienced this problem in a house I recently bought. I moved the softener bypass valve into its bypass position. Problem solved -- though took a bit longer for hot water to stop smelling due to hot water heater tank.

My water is fine without the softener. I plan to get rid of the equipment.

  • Thanks for the response Jeff, I'll turn on the water softener bypass and see if that solves the problem. We definitely need the softener so if the smells stops with the bypass I'll look at cleaning it out. Looking in the tank where the salt goes its totally clean. Is there another area that could need cleaned? Apr 14, 2021 at 15:26
  • Jeff: That may or may not work. Julie's best bet is to get her water tested before any treatment. That way, she'll know what she is dealing with. Unfortunately, there aren't very many experts in water treatment. A standard water softener from a big box store might be the exact WRONG solution. She should try and find the best specialist possible for help and evaluate her current treatment system. In the meantime, maybe just bleaching the system will fix it. Again, many variables and unique situations. Apr 15, 2021 at 21:33
  • Closing the bypass valve is an easy test, though. That's why I suggest doing it before taking any other, more difficult / costly, measures. Apr 16, 2021 at 13:59
  • 1
    Jeff, I just tried turning the water softener bypass on and let the water run through for a minute and it quit smelling! I'm shocked if that is the problem, because my water softener tank always looks completely clean when I fill it (although my bf filled it last time & he doesn't remember if it looked dirty or not). I'll have to look into cleaning it or having someone come out to check on it. My water hasn't seemed soft for quite a while even though we've had the tank filled for several weeks now, so I wonder if we are having an issue with the softener system. Apr 17, 2021 at 2:37

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