Making your own water is not cheap, but it may be worth while if dockside water is not available, inconvenient or poluted. Basic RO (reverse-osmosis) desalinators are not complicated, but they must be used regularly or "pickled" to prevent membrane damage (I think that's what Fred is refering to).
I have a no-frills 10 gal/hour water-maker from Quality Water Works
(pics below). This is a relatively inexpensive setup because the components (hi-presure pump, membrane, valves etc) are all available over the counter. George Walker, who founded the company, answers all email personally and is very helpful. I agree with Larry M about AC not DC although driving the hi-pressure pump off the engine (belt and clutch) might be worth considering, depending on your cruising style.