My upstairs walk in tile shower leaks to my 1st floor only when we shower

If it is a "shower" it would leak when you use it if the tile grout is possibly bad, the pan is cracked or the wall valves are leaking. You will need a plumber to look it over.

Hi Mary! Ma0641 is right in that this is probably a job for a plumber, but if you are handy, you could do some basic investigation work before the plumber arrives!

Here, I would suggest that you start by filling a 5 gallon bucket with water from another tub or shower and then pour that bucket down the drain of the tile shower in question. I would repeat this a few times in succession and see if the drain leaks downstairs. By not using the shower valve and testing only the drain itself, you can be pretty sure that the shower pan or drain pipe are the issue(s) at hand IF the leak shows up after this "TEST", right?

If this test fails to show a leak then I would suspect that the shower valve or the tile walls may be the culprit... ;)

Start there... post back with results, OK?

Mark