by Jim
(Leamington Spa)
Water pumps through taps and also comes out of some sort of overflow pipe under the caravan when I turn the taps off it carries on pumping out of this pipe until the barrel is empty even with the main switch off.
I think you will find the tap to drain your water heater or on board tank is open and needs to be closed. If can locate the tap and close it, I think this should stop your water draining away.