Water Leak From City Water Connection

If I am understanding you correctly, you have a little plastic check valve/back flow preventor in the place where your water supply hose enters your rv? Commonly, you will get a little debris in those valves which will cause them not to seat properly. Take something and activate the valve and work it back and forth a few times. I can use my little finger on ours. That often knocks out what is causing the leak and ends the problem. Otherwise, replace or use the cutoff valve suggested in one of the above posts. I have done that also.

PSW
2013 Phoenix Cruiser 2350
Motorhomes since 1982