Thanx for the added info, Joanne; that narrows the likelihoods down to basically 3; I'm guessing this pipe is fairly small, maybe 1" diameter, and is probably-
- a condensate line from furnace, which would raise question about why it's wet, as you don't have A/C running.
- a drain from a humidifier on the furnace
or an extension from the T&P valve on your water heater, which is what I suspect from what you've said.
On the side of your water heater, usually to the right of the temperature controls & almost to the top of the tank, you'll find a brass relief valve, which has a small handle dangling from it, and it should have a small pipe leading downwards from the valve. See if this pipe doesn't then elbow and go out the wall; if so, this should be the answer, but it's a warning since it's been leaking water.
If this is the right pipe, the T&P valve is bleeding off water; either because the valve is failing, or there's a need for service or replacement of your water heater.
Another possibility would be if your water heater is on a platform above the garage floor level, it may have a leak safety pan on the platform, which is then piped out the wall. Water draining to this pan could also be from the T&P as mentioned, or from the water tank, meaning it's time for a new one.
Follow those leads, Joanne, and see if we have found the culprit. Good luck!