My well water tasted and smelled fine until I had new faucets installed. Since then there is a strong nasty gassy kind of smell coming from the COLD SIDE ONLY, and ONLY IN THE NEW FAUCETS.

This smell is NOT the common sulfur egg smell often found in well water. Water from the old faucets that were not replaced does not smell. Water from the hot side of the new faucets does not smell. Water out of the garden hose does not smell. Only water from the cold side of the new faucets smells. My very experienced and excellent plumber said it was the faucets--"some new faucets cause this smell and some don't," but he does not have an explanation. It is a disgusting smell and water must be run and wasted every time the cold water is turned on to get to the regular taste of the water. I want to know what is in the manufacturing of these new faucets that is causing this smell? Could something in the materials of the faucet be reacting with some element in the water to create a gassy smell? This smell behaves like a gas too in that the smell is very weak in the cold side of the faucet in the basement bathroom, strong in the ground level bathroom and kitchen faucets, and strongest in the upstairs bathroom. What are the manufacturers putting into these faucets? Is it harmful? Where are these faucets made--China? Is there anything that can be done to modify the faucets that would get rid of the smell? Why is it only in the cold side? Is the only way to fix this problem to buy new faucets? How can I tell I am not buying another new faucet that will cause my cold water to smell? Is there a list somewhere of blacklisted brands to avoid? I would like to hear from others with this problem and from anyone who has some answers. Thank You,
shellycross

I am an electronics Tech, there could be something bad making it through without inspections from another Country.
I would maybe swap the Hot and Cold lines under the sink, so Hot water goes through the
Cold faucet. Run very hot water through. Maybe the heat will help loosen or flush out the
Chemicals? Or lubricants?

This gives me the idea that the odors are being picked up from the plastic. Sure enough, this link shows that it's true:

Water Picks Up Odor From Plastic Pipes - healthfinder.gov

Plastic Water Pipes Affect Odor And Taste Of Drinking Water

Doing a Google search with "removing odors from plastic" gave some results, none 100% useful.

It might be the fixture. It might be plastic piping if it was used. I know you don't want to think of it as "New car smell", but it will probably eventually go away.