Are you shure that is the fresh water system? Do you leave your sump pumps breaker on all the time? On my H46 I have 2 sump pumps that collects water from the drains of both showers and the A/C drains (which I conected myself to the sumps). The sumps drive me crazy at night because the switch is very sensitive and runs like you describe every few minutes. The forward one is the one that bothers me the most but I think both of them do the same thing. The one in the middle of the boat is near the fresh water pump.