Carver 355 leaking fresh water

You have a water heater under the floor board by the dinning table, a shower sump pump, and a vac head. I would eliminate all the above and shut water supply to boat from dock. See what happens you also have a drain for the a/c going to your sump pump to. The diesel fuel could have happen when changing fuel filters and you spill some.

a couple of guesses
condensate from running your ac. on my 405 which is basically a stretched version of yours the fwd ac is under the fwd berth it does go to a sump pump but maybe the pan drain is clogged or hose is loose etc then draining into the fwd bilge

if you turn on your fresh water pump does it cycle every few minutes even if no water is being used anywhere? which would indicate a leak in system somewhere
or
sump that isnt operating properly and overflowing

Put some food coloring in your water tank and start turning things on. You should know pretty quick where it's coming from. If you still have water with no dye it would be from your shore connection in.

I kept getting water in the bilge of my old 355. Ended up being the water heater had a small leak. Ended up rotting the floor and it was leaking underneath and I never could tell that it was leaking. Might be worth the check.

I noticed that my fwd sump started running every 5 minutes tonight. This was the first time i had ever connected dock hose to water system.so i checked and found that the fwd sump was slowly filling up. I googled this and found this post. So, i shut off dock supplu, shut off a c, pressure water pump was off yet thw sump continued to fill, and fwd bathroom floor is dry. The sump pump is new and all clogging left by previous owner has been cleared, but it is stilll filling as i watch it, and i have nothing on.
Only 2 places i can see hoses going in. 1, the shower floor drain ( black) and another white hose (smaller) connected to that same fitting.
Everything is off, but it keeps filling.

Also, could it be the exit water running back down the pipe into the sump

P S , one more comment.
The fwd bilge under this sump tank is, clean, dry, and not filling

It might be a condensate drain from an air conditioner.

Thank you to everybody that responded to me. I spent two hours checking all the different alternatives. Then I took the sump motor out and saw that the one-way valve inside had a piece of crud a quarter inch. The pump at work low everything out through the whole load would go down And shut the pump off. Then all the water remaining in the holes going up to the outlet was slowly trickle its way back down into the sump start the procedure over again this is good information for anybody else to know for a similar problem in the future. Thanks again