Each time the downstairs tub is used, the carpet right outside the bath door gets wet. The drain is in the same wall but it is not leaking behind the drain. Our bath is two rooms (one with two sinks has carpet, the other with tub and toilet has tile. The carpet gets wet right the tile and carpet meet. The tub is through the door and to the right of the wet spot.

Roof leaks and drains can all have leakls that surface many feet from the actual problem. If the wetness only happens when the tub is used it's a drain leak or a faulty outlet on the mixing valves. What is directly below the tub?

It sounds like your valve in the wall may be leaking each time you turn it on, or your waste and overflow pipe may be allowing water out.

Here is my suggestion to find the answer.

1) Fill a pale 5 gallon pale of water from another water source (kitchen) and dump into the tub that might be leaking. If water is THEN found soaking the carpet then you know that it is indeed the waste pipe connected to the tub. If it does not leak... THEN plug the tub drain, and turn the spigot or show on. If it leaks then, THEN it's the shower valve. If this does not seem to resolve which one creates the leak, then start by removing sheetrock to expose the waste pipes and enter the wall behind the tub. Sheet rock is the easiest and cheapest repair.

Good luck.

-Wade-