I agree with everyone that advises against this. But... I also understand how convenient it is! The main reason I like to hook up (I have not attempted on my R23, and probably will not for various reasons) is that the Admiral and I like to shower early in the am, and when you're in a nice quiet marina and the water pump is cycling... it's pretty loud outside, and I like to respect my neighbors' quiet time :mrgreen:
The issue I found is that every marina I visited had static water pressure that was too high for my comfort, especially since many boats are outfitted with John Guest fittings on PEX (push-type connectors), which can be susceptible, albeit rarely, to vibrating loose. I would never take the chance on putting medium-to-high water pressure (50# +) on these systems. In my many years in the plumbing industry, I have seen many push fittings fail.
For this reason, I would always carry a pressure reducing valve outfitted with garden hose connections so regardless of the marina's static pressure, I could always count on my boat getting no more than 25# (lowest setting on the one I used), which is more than enough to handle anything you'd use on your boat, but not so high that it may compromise the boat's fittings.
But as others stated: Always turn the main valve off when leaving the boat! 😀