There is a smell and bad teste coming from the cold water when you first turn it on, it goes away after 10-15 sec. But when you turn it off and let it sit the smell comes back. I have well water. I went under my house where the well line comes up and goes to a brass T. On one side of the T there is a copper line goes to the house shut off and on the other side of the T, a copper line goes to the a 30/50 control box then to a water spicket, then to the pressure tank. When I turned the water spicket on, the water does not smell and teste bad. Can you help me

A quote from Water Quality: cold water odor

Perhaps it might help. I hope that it does.

Thanks for askiing.
Without doing an on site analysis, I can't advise you on that. However you should know that any foul smell could have a bacterial cause. Therefore I would recommend a bacteria test by a certified lab and a complete water analysis.
You can go to water, water quality, NSF Certified, certification, iron in water, nitrates, rusty stains, blue green stains, water filter, pure water, water contamination, clean water, water problems, e-coli, lead, cryptosporidium, bottled water, well water, water and find a WQA Certified Water Specialist in your area who can help you with that.

It would be a good idea to use safe bottled water for consumption until you have your water checked out.

If it is simply an aesthetic problem you may get away with a simple filter. Otherwise you may need constant disinfection. A good specialist can best advise you.
This doesn't sound like a DIY fix. Get a professional's help.
Good Luck