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!
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.
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.
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
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.
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.