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I live in a brand new home. Since we moved in (Nov 2015) there is a rotten egg smell in just one of the bathroom sinks and just from the cold water. It used to be now and then. Now it is 90% of the time I get that smell in the cold water. What can I do? The builder sent a plumber out who basically cleaned out the top of the drain and said it should go away. I was doubtful and it has never gone away and is now more the norm for the cold water in that faucet. Help!

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    How many other cold water faucets are nearby and unaffected? Might there be something in the faucet aerator? Might there be something stuck in that one pipe? You might consider disconnecting the faucet from the cold water supply and running the water as quickly as possible (e.g. into a bucket) and see if anything else comes out. – Daniel Griscom Feb 27 '16 at 18:41
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We had this same problem. The smell was only coming from our kitchen sink, and only for a few seconds after the water was turned on. No other faucet in the house had smelly water, so I was quite certain it wasn’t from water heater issues. We tried draining some water from the water heater just in case, but no sediment came out and no smell. Since the smell only lasted a few seconds at the faucet, I figured the smell had to be building up somewhere between the water heater and the offending sink.

What I eventually noticed was that the braided pipes leading to the hot and cold had subtle horizontal “S” curves in them where smelly gas could get trapped, like how a toilet is shaped so sewer gas doesn’t come back up. I figured that when the water hadn’t been run in awhile, the gas would build up in the upper curve. Then the water would push the gas out when it was turned on. So I replaced the braided pipes with shorter ones that didn’t crate that “S” curve. We have been smell free ever since.

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here. – Daniel Griscom Apr 15 at 14:58
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Are you on a well?

Sulfur (rotten egg) smell can be caused by a few things, like the content of the water, something decaying (like in a drain) or by bacteria that can live in water supply systems. The bacteria are harmless but can generate a rotten egg smell, and the sulfur they release can build up in little-used plumbing.

Water wells are more likely to have this problem. If you are on a well and get the odor anytime the plumbing sits for a few days, you can have the well sterilized and flushed (usually by turning it off, adding several gallons of bleach to the well head and letting it sit for a few hours, then flushing ALL of the plumbing for several hours.

Since you are describing a single fixture, it could be a problem with the plumbing to that fixture only. I don't think there is an easy way to sterilize a city-service attached plumbing system, and there may be risk of backflow that would make it illegal or inadvisable.

You could also just try running the sink for a long period of time to completely flush the line.

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  • Even if you shock the well system with bleach, the bacteria will likely return and repopulate. In this case, a chlorinator system can periodically drop chlorine to keep the bacteria at bay. – Sam Jul 22 '19 at 13:19
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Try Replacing the Filter for the Water Softening System

I had the same issue and after reading through the answers I decided that replacing the overly looped water feed to the cold water was the way to go. It is hard to reach because of my setup so I jiggled it and then went looking for wrench.

Before I got to that point I replaced the string filter in my water softening system (well water) and after replacing it the first faucet I turn on had a stronger flow. So I went back upstairs and turned on the cold water and low and behold all kinds of nasty junk came through and down the drain. Bad smell is now gone!!

Side Note: I will probably replace the feed eventually since the smell may return if more junk gets stuck there but for now problem solved!!

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  • Hello, and welcome to Home Improvement. This is interesting, but doesn't answer the original question. – Daniel Griscom Apr 20 at 15:45
  • I find this an answer, which is to replace the filter for the water softening system, though it could be written in more of an answer format than a shared experience format. – Ack Apr 20 at 16:27
  • @Ack op does not mention having a water softener – Kris Apr 20 at 17:03
  • @Kris "my water softening system" – Ack Apr 21 at 1:10
  • @Ack 0P refers to the original post – Kris Apr 21 at 2:05
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If the Plumber decided to do just the drain, then I'd be inclined to follow his lead. It could be a mold or bacteria in the drain, but more specifically in the overflow's throat.

Hot water would usually steam the smell away & cold water would fan it around. Try dribbling in bleach while scrubbing inside the overflow & down the drain, stopper removed, as completely as you can with a long & small bottle type brush with glasses or safety glasses on.

Check the brush periodically. If the brush comes out black or really with anything then you're in the right area & keep scrubbing until the brush comes out clean for both holes. The bleach should take care of anything further down the drain under the sink too. But, you can also monkey around down there if you want a thorough mess.

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If I was in a home less than 6 months old I would insist on the builder rectifying this problem ASAP. - Incidentally if it was a well problem it would affect ALL cold water faucets,not just one

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This smell is common to lavatory sinks. You must block the drain from inside the sink but below the holes in the drain that allow the overflow to function. I do it with a coat hanger with enough clothe attached to it so I can remove the pop up waste lever (with the ball on it) that allows the drain stopper to either close or open. Remove the stopper and stuff the clothe on the end of the wire close hanger to prevent the water from draining. Fill the sink to the overflow and as it fills over the overflow opening, pour a cup of bleach into the overflow with the water that is rising. Shut off the water and let it set for a few hours. Repeat the pouring of the bleach if the water leaks out through the drain below. You must repeat this maybe every 90 days so put it on your calendar. All the best.

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Cold water only sulfide odor may be coming from the supply hoses under the sink. Apparently these Chinese plastic hoses react with something in the water (bacteria? ). I replace the hoses every six months. Working with city water to try to figure out the source. This is a 2 year old home.

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