Allan from from Chatham County, NC wrote in about a very particular rotten egg smell problem, one I have yet to encounter.  Below is the string of emails of Alan and myself communicating about this problem.  It’s an interesting one, and worth the read if you are having some localized rotten egg smell problems in your plumbing.

My wife and I live in a small 30-year old house with well water
and copper plumbing, a 17-year old 80-gallon hot water heater, and a pretty
standard inline cartridge sediment filter.

Recently, we started noticing a rotten egg smell (probably hydrogen
sulphide?) coming from ONLY the upstairs bathroom sink COLD water tap after
several hours of not being used.  The smell disappears quickly after 5-10
seconds of running the water.  The taste of the water appears to be
unaffected.

I’ve checked all the other taps throughout the house (hot and cold
including the toilet tanks and bowls, bathtub, shower, and clothes washer),
and none of them have this smell, even after much longer periods of not
being used.

My thought on an inexpensive remedy would be to remove the sediment filter
case and cartridge, fill the case with clorox, and temporarily reinstall the
case without a new cartridge.  Then, I would turn on only the affected cold
water tap upstairs until I smell chlorine.  Just as soon as I smell the
first traces of chlorine, I would immediately turn off the tap, thus
trapping a fair amount of chlorinated water in the affected line only.  I
would then wait, say, overnight for the chlorine in that line to do its
anti-bacterial duty.  Then, the following morning, I would turn on the cold
water tap again to flush out all traces of the chlorinated water.

Sound like a plan?  Or does it sound like a plan of someone who’s way off
base?

Thanks in advance for your reply.

Hi Alan

Usually, the rotten egg smell (hydrogen sulphide) comes from one of two places:

1) Directly from your well.  The bacteria can usually be found deeper in overburden aquifers

2) From sewer gas escaping through your drain pipes

It could be that you have some biofilm accumulated in that line, and some of the bacteria are of the sulphur reducing variety.

Your original plan is a good one, if that is indeed the problem.  The only thing I would add is to run water vigorously through the tap first, to create a scrubbing effect with the water.  Make sure no other tap or appliance that uses water is on, and open the tap full on for 5 or 10 minutes.  This might produce enough velocity to start breaking up the biofilm, making your chlorination process more effective (as chlorine is only a surface disinfectant).

Thank you very much for writing in. I’m grateful you did as this is a problem I’ve never heard before.  Please let me know how you make out.

Problem solved.  Here’s what I did:

• Before bedtime on Sunday evening, I removed the 10″ cartridge from the filter case and filled the case with 100% Chlorox.
• I reinstalled the case without a filter and reopened the shutoff valves.
• I went upstairs and turned on only the cold water tap to the bathroom wash basin (the culprit producing the smell) and let it run until I started smelling chlorine gas.
• I immediately turned off the cold water tap and we went to bed.
• When we got up on Monday morning, I turned on the cold water and let it run to flush out all the Chlorox.  I also turned on all the other cold water sources in the house to hasten that process.  There was quite a large amount of ruddy brown water that flowed for quite some time, but then it gradually disappeared.
• When the Chlorine smell and the ruddy brown water had disappeared, we began using cold water again.  I then installed a new 10″ filter.
• We then went to work for the day at about 7:30 a.m.
• When I returned from work at about 6:30 last evening, I immediately went upstairs and turned on the wash basin’s cold water.  No smell whatsoever.  The smell normally had reappeared after about three hours of nonuse.
• Again this morning, no smell.

Looks like the problem may have been somehow isolated to the cold water line to the upstairs wash basin.  But that doesn’t explain why there was no smell to the toilet water tank, the shower, or the bathtub water faucet, all of which receive their cold water from the same cold water line.  My best guess now is that somehow, the faucet assembly, which I replaced about a year ago, somehow became contaminated.

Thanks for your help.

Great to hear it worked.

There very well could have been some contamination when you changed your tap.  We live in a bacteria world and contamination happens very easily without you knowing it.

One of our standard municipal procedures is to disinfect any and all plumbing and fixtures if the system has been opened to air, to do a repair or replace a fixture, for example.  It would be a good idea for you to do the same if you do any other work like that because you have your own well supply and there is no secondary disinfectant in your water.

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