I left town for a week and now have a hot water heater that's been sitting and apparently breeding bacteria resulting in an abundance of hydrogen sulfide. It stinks really bad.

I tried emptying it and there was some slight improvement but after 24 hours the stink is back.

I'm now thinking about chlorinating it. Various articles I've read suggest draining a bit of water, removing the anode rod and pouring the bleach in there. I have a different idea and was hoping for some feedback about whether or not this will work and any potential factors to consider.

Immediately before the water heater I have a small 10" sediment filter housing. Can I simply pour the bleach in there and run the hot water to draw the bleach into the water heater? It seems like a simple enough approach but as I wasn't able to find anything online about doing it this way, I'm feeling a bit tentative.

  • The bad odor may or may not be due to bacteria. Some wells may produce sulfur compounds that are more noticeable after heating. See what others in your area do about that issue. Commented Aug 19, 2019 at 6:31
  • Hi @DrMoishePippik - the bad odor is due to bacteria. Commented Aug 19, 2019 at 6:41
  • Excess air can also cause problems, I would fully drain the tank and refill now make sure the temp is hot enough if up around 140 nothing will grow even with extended times of no use.
    – Ed Beal
    Commented Aug 19, 2019 at 14:52
  • @EdBeal - thanks I am aware of that and the thermostat has been set at around 145 for years. I just checked temp of water at the tap and it was around 138 which makes sense since it would have lost a few degrees traveling through the pipe. To be on the safe side I truned it up vloser to 150. All the said, these comments are a bit off topic. This is not a question about how to address smelly water. The question is about safe ways to introduce chlorine into a hot water heater. Commented Aug 19, 2019 at 16:54

1 Answer 1


If I were to add chlorine to a water heater I would add it through the anode port, this would be a good time to verify that the anode is still serviceable. After letting the treated water sit I would flush through the closest hot water faucet and once the majority of the strong chlorine is gone flush all the hot taps to prevent chlorine poisoning. My well guy told me of a family that saw him bleach the well and did not realize he flushed the well for 3 hours after waiting 3 hours. Almost killed 2 or 3 of them. So be careful and flush the tank until almost no smell.

  • Thanks, not the answer I was looking for but after reading a bit about anode rods, I think this is sound advice. Apparently a zinc anode rod will help with the bacteria as well. Commented Aug 19, 2019 at 18:11
  • I guess I would be interested in your different ideas. Pulling the anode would be safer leak wise than the inlet or outlet lines to the heater, I guess you could even pump it in from the drain valve at the bottom of the tank so I fail to see what other advice I could provide as these are the only ways to add and the anode would be the easiest plus the fact that they should be on a routine inspection schedule.
    – Ed Beal
    Commented Aug 19, 2019 at 18:21
  • What about adding it through the filter housing per my original post? You offered good advice here but did not answer the question. Commented Aug 19, 2019 at 18:36
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    Ed, I'm referring to this very post. The entire last paragraph explains about the filter housing — perhaps you missed that part. In regards to potential damage, it appears you're correct. The sumps are typical blue housings made from polypropylene which is not particularly fond of chlorine: calpaclab.com/polypropylene-chemical-compatibility-chart — nevertheless, the bleach would only be in contact with the housing for a few seconds before getting flushed through. I've bleached out my undersink housings before without any detrimental effect and with a great degree of success. Commented Aug 19, 2019 at 19:35
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    Ok brain fart on my part I read that 2x and over looked it both times. You will have to flush all your plumbing and run enough hot water to get the chlorine in the tank. But you should check the anode if it is gone and there is electrolysis starting in the tank it could be the source of the smell and say good bye to your tank in a short length of time so why not just put it in the tank to start with no guess work on how much made it and less possible damage to the filter housing.
    – Ed Beal
    Commented Aug 19, 2019 at 23:38

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