Before we moved on board full time we kept sv Watermelon on a mooring, and each weekend when we went out to her I was so relieved that she was still afloat!
My worries were just a tad overblown. Not because of our bilge pump setup, which was pretty standard, a 500 gph pump with a float switch.
When we left the boat every Sunday night we went around closing all the through-hull fittings. Not only did that close the holes that could let water into the boat, it tested those through-hulls, something that took a lot more discipline after we moved aboard.
If you have been aboard your boat while a survey of the boat was being done, you might remember that the surveyor checked each of the through-hulls, and tested each one as well to make sure they opened and closed easily and didn't leak. Although I don't have any data to back up this theory, I think that failed through-hulls are the major cause of a boat sinking on its mooring or in its marina berth. Each of our bronze through-hulls was bonded to the boat grounding system, and our zincs were inspected frequently and replaced before they were completely gone.
After all, if a through-hull fails mid-week, by the time you get back to the boat the battery will have been run down to nothing, the pump will have failed, and your boat will have sunk. Better to close those holes and leave the pump to take care of the trickle that might seep through the shaft seal, or some unknown deck leak.
We now have a power catamaran, and some of the issues on the sailboat repeat themselves on the power boat. We have a hot water heater that heats the water through a heat exchanger with our engine cooling system. The water gets really hot, and one of our mistakes has been not turning off the fresh water system when we were running the engines. Another was forgetting to make sure that the bilge pump switch was switched to "automatic".
When the water in the h.w. heater gets really hot and pressure builds up, the excess pressure blows out water through the pressure relief valve. If the water pump is left on, the pump refills the water in the tank, it heats up again, the expansion blows out more water, and over an 8-hour period several gallons of water are spilled into the bilge. Though the bilge pump switches are usually on "automatic" they are rocker switches that occasionally get rocked the wrong way, to the "manual" setting. Imagine the dismay when going into the engine compartment to check the oil and find water in the bilge. Fortunately I'm not afraid to taste the water to determine if it's fresh or salt, so we know what happened pretty quickly, or at least what we were looking for.
And then there was the day that we forgot to turn off the pressure water switch, made an 8-hour run, and discovered that even with the bilge pumps on automatic we still had water in the bilge. That time, it turned out that one of the bilge pumps had failed.
Complacency is an affliction that hits us all at some time or another. That bilge pump worked perfectly for several years and we stopped thinking about testing it occasionally.