There is a 1/2 copper pipe coming up from under the foundation of my house that just sticks out of the ground about 12 or so, and what I believe is 1 1/4 PVC pipe coming from the water heater (maybe a drain?) and doing down the same hole. The hole is plugged up with firestop, but I‘m trying to make the closet the water heater is in a little easier on the eyes, new paint, etc. Is this copper pipe still in some kind of service? or could I cut it off and fill it, too, with firestop before painting the closet floor (bare concrete) with some kind of concrete/garage paint?
The advice of William B above is good. You usually should have a professional help with plumbing problems. The copper pipes may have a union, If so it becomes much easier to fix. A union looks like one big nut (2 or so)with two smaller nuts on either side (1 or so) If not it will take a torch, solder and some new fittings. If you decide to fix it yourself,turn off the water at the valves above the water heater. If their is a union, use two wrenches to loosen the nuts. Once undone, you should be able to undo the pipe going into the water heater. check it for any problems, rust corrosion, etc. If it is just loose, get some teflon tape and wrap it on the treads and retighten the pipe. Then connect the union back up. Make sure you use two wrenches and tighten pretty well. It is best to have help of someone who has installed a water heater or done plumbing work to help.
I would guess that the 1/2 inch copper pipe is either an old supply line or a line that used to run to an outside faucet. In either case, if the end of it is not plugged or capped off, cutting it off shouldn't hurt anything. The other pipe should be a 3/4 inch pipe from the pressure/ temperature relief valve on the tank and should be running to a drain or an area where flooding will not harm anything, such as an open crawl space. If the end of that pipe is just open to the floor of a living area, it could cause a major flooding situation if the valve ever pops off. You really should have it routed to a place where water won't hurt anything.
The PVC coming from the water heater is from the temperature and pressure valve (TP). That line is normally fed to a drain if the TP valve goes off. I'm speculating the pipe just goes below your house. I'm unsure why you would even firestop that unless the person doing it was told to fill every hole and by golly, they did it :). The copper may be a stubbed water line (even though that doesn't sound right). Other than that, I would not even venture a guess unless the 1/2 copper is for a condensate drain from your furnace area. Normally you would have a conventional floor drain for that purpose.
