pumps would be run from a [or multiple] generator sets which in turn are run from oil fuel, as said somewhere earlier in this thread the bigger continer ships do carry VAST quantities of this stuff so should have power for a long time if your not going anywhere, these days most new vessels have water recovery plants to make potable water form the sea, and sewage plants so there not dumping raw sewage overboard.
Growing food onboard? this will take soil, so theres the difficulty of ferrying out a few tons?? not sure how much you'd need - then distributing it evenly, so there's no stability problems - unfortunatley you can't just go and dump a few tons on a vessel and not think about it - it may just be a case of filling/ emptying the ballast tanks a bit, but then again it might not be.
You could dump a few hundred tons on deck of a small freighter without the boat noticing it.
Heck, we brought our barge over the north sea (and this barge is tiny compared to any freighter), we put a 1000l fuel tank on deck and filled it - you couldn't even see the boat shift as the tank was filled.
If living on board a freighter, I'd set up composting toilets - they could be quite basic. Chickens for eggs and meat. A couple of feet of soil in 'raised beds', some greenhouses built over them.
Where would I get the soil from?
Easy - drop a digger on a workboat, motor up a river and nick it from the riverbank!
Mooring up the freighter in the humber, it would be very tempting to rig a waterwheel for some power generation - the tides run at 5-6 knots in places.
