Originally Posted by TARVIDSON
My water pump runs a little faster with the generator on than just with battery so I am guessing something is loose on the pump mounts or something nearby that is noisy when it is running just a bit faster. Anyway getting the gen going and water running when you can stabilize the pump and pieces around it with your hand will probably tell you if it is the pump, a loose fitting etc.
The water pump is a DC motor whose speed is effected by the voltage applied to it. When you're using a generator or hooked up to shore power, the converter should be holding the RV's DC voltage above 13V. On batteries, unless they're fully charged, you'll always have less than that and the pump will run a little bit slower.
If there's a significant drop in the water pump speed when running only on batteries, I'd take a careful look at the battery quality. RV house batteries should be tested using a deep cycle load tester, not an automotive load tester. My RV had both 12V house batteries fail within a year as a result of improper storage and a shorted entrance step controller but when they were tested with an automotive load tester, they tested good. The batteries had less than 50% of their rated capacity when deep cycle tested. The automotive tester only tests the ability to produce a large current (hundreds of amps) for a very short time, not the type of load you have on your RV's house batteries.