Welcome to the forum
Is the moisture from the water heater inside the trailer? If so I would check all the fittings for any leakage. There shouldn’t be any moisture inside the trailer at that area.
If your hooked up to city water and the fresh tank is filling up, your water pump is most likely leaking at the check valve. You may be able to turn off the city water, run the water pump for a couple minutes. Then turn it off and turn the city water back on. If it doesn’t fix it, you’ll need to fix/replace the water pump.
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2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.