Those ShurFlo water pressure regulators are so common for boats and RV's that I think if they were highly prone to failure where they'd allow unlimited flow-in and flood the boats, they'd be sued to like crazy and either change the design or stop selling them. They do fail of course -- I can buy one here for about $60 and they don't last forever -- but in my experience when they fail they usually stop the flow to a trickle, or entirely. Oddly and coincidentally, four boaters on our dock had to replace them this summer, but then all four boats were late 90's. When we bought our 1996 boat in 2015, that was one of the first replacements I had to make. I remember we were coming up the Hudson and fortunately Shady Harbor Marina had a spare in their marine store. I did have to clean the screen last summer -- it was full of bits and gross stuff. Didn't make me very confident about the city water purity, but then it could have been junk in my own shore water hoses too.
The pressure regulator aside though, like some others I'm a fanatic about not leaving an open shore water line connected to the boat while we're gone, or even away from the boat for dinner. Hoses can fail, hose clamps can fail. I'm pretty sure my three bilge pumps could keep up but I don't want to test that theory. It's not hard to be cautious. I put a garden hose valve on the quick-connect so when we leave even for a long dinner I'll just close the ball valve. And when we leave at the end of the weekend I always disconnect the hose entirely because I don't trust visitors or dock neighbors or kids to not touch our supply valve on the dock.
And then one other thing while we're talking water supply and (some) Mainships. I have a cruiser model, not trawler style, but I had a water problem I had a very hard time figuring out so I'll mention it here in case this is ever helpful to anybody. For a while our boat developed a significant list to port and I couldn't figure out why. Our fuel tank is midships, so that shouldn't have done it. After a while I noticed water dribbling out the water tank vent cap on the port aft quarter of the boat. I finally read the schematics and realized there was a check valve between the house water line and the 100 gallon water tank under the master berth on the port side. That check valve had failed so every time we connected shore water, it would fill that port water tank to the top and then push water up the vent line and run out the vent cap. So the port tank had over 800 lbs. of water in it, while the starboard water tank was almost empty, hence the list and the water running out of the vent cap. Anyway, so many things can go wrong with the water supply system on a boat I never leave shore water on or connected when the boat is unattended.