I don't have ideas that will find the leak while keeping the ceiling dry unlees you open the ceiling or a wall. Remove shower head and cap off the pipe. Threads on pipe are 1/2 inch male pipe threads. Turn hot and cold water on then pull excusions out and look for leaks around facuet stems. Listen for spraying inside wall or drip in ceiling down stairs. If no sound is heard, wait 30 minutes to see if ceiling becomes wet. If those tests are good that leaves drain couplings,drain pipes and cracks in inclosure. If you have a door rather then curtain examine lower track closly. Water can run down door into track where it leaks around screws holding track to stall. Come back if no joy and we will go deeper.

Okay - this is beyond my level of plumbing expertise. Time to call in a professional.

I believe that the damage to the ceiling is already enough that replacing part of it is necessary. So start removing a limited part where the water is appearing. After the cause of the leak is discovered and verified as being corrected, repair the ceiling. Call the plumber if necessary after you know the source of the water.
The plumber probably would start by cutting into the ceiling.

Cutting into the ceiling is fine if that's what needs to be done. We have sold this property and this leak needs to be properly fixed. Water softener also bit the dust so I can probably have the same plumbing professional take care of all of this and then get someone else to patch the ceiling. If it wasn't sprayed it would be easier to patch I think. Matching up a sprayed ceiling seems to not work too well from what I've seen.

Yes, I understand. If surgery for cancer was required, the major concern would be the surgery scar. Sometimes we major on minors.
Worst case, a piece of drywall could be fastened in place to replace the piece removed and then the entire ceiling could have another layer of drywall applied over the original. That new layer could be finished smooth or sprayed.
Anyone choosing to spray texture on a ceiling probably needs serious mental health treatment.
OK, I admit that today has had lots of issues arise and my mood is not good.
Would you consider that if the leak is not properly identified and repaired, the ceiling will eventually fall of it's own volition?

This post was edited by bus_driver on Thu, Jan 8, 15 at 17:21

Thank you kudzu9. You do make me think I just need to call a good plumbing repair guy and have them take a look at it rather that continuing to speculate when I'm really clueless. They can hopefully get to the bottom of it quickly.

gibby-
You're welcome, and good luck. I was puzzled by my neighbor's leak until he said: "Let's cut out some of the sheetrock in the ceiling below because I want to see what kind of water damage has been done to the joists." We cut out about 3 square feet. Fortunately, there was little wood damage...just soggy sheetrock. Once we could see up in there with the shower running, the source of the problem became much easier to figure out. Bear in mind that water can move laterally, so the leak may not be directly above the point it appears to be coming from.