We have a sulfur rotten egg smell coming from the cold water faucet only and only in one bathroom. We have city water. We removed the faucet, check the drain, no smell.
But the water emptied from the flex hose warm side no smell at all. Cold side, smells like rotten eggs. Still am not sure where source is. Any ideas?

Sounds like you have bacteria growing in the cold water supply. Let's track it back. Shut the water off at the house shut off and remove the smelly faucet and soak it in a pan of full strength bleach. Do the same with the angle stop and the supply line. You should be left with a copper stubout with a chrome nut on it. Now hold a pan under the stubout and turn the water back on for a second. Does the water smell bad coming out of the stubout? If no then reinstall the angle stop and faucet since they have already been sanitized. If the water still smells then click on back and tell me about it. Good luck, Tom

We have a sulfur rotten egg smell coming from the cold water faucet only and only in one bathroom. We have city water. We removed the faucet, check the drain, no smell.
But the water emptied from the flex hose warm side no smell at all. Cold side, smells like rotten eggs. Still am not sure where source is. Any ideas?
Took the faucet off last night. It didn't smell at all. Like we said, the cold water from the flex hose that we emptied into a jar, stunk. The hot water from its flex hose, did not stink at all. Definitely the cold water. Will try and let you know. Thanks

Change the flex hose, some have a rubber/plastic liner, it can go bad... especially if made in good old China. Good Luck. Jim

OK, I had the very same problem (Rotten Egg smell on cold water faucet only in only one bathroom in the whole house). Although I though it wouldn't work, I did what jrg973 suggested and the smell is gone. By the way, where do you get anything that isn't made in China?? I sliced the old flex line open and found a black film even though I couldn't detect any smell. Is there really any company left in the USA that makes plumbing supply products?? Ed