We always turn off the water pump if using our water and always turn off the campground water if leaving the rig. Too many cases of hose fittings popping off and flooding. What the others have said about keeping the valve closed until you are ready to dump is very important. Since its their water and their septic or sewer, run plenty of water into your tanks so you have a lot of liquid to carry the solids out. If you were traveling with the rig it would get agitation and break up the solids but that doesn't happen when parked all the time.