I always seemed to run out of water before I ran out of diesel
. I soloed and had a 100gal/400L tank. A 6-gallon/24L Sunshower rinse lasted me 3 days (wash in salt, rinse in fresh). I allocated about 1gpd/4Lpd for personal use, dishes (again, wash in salt, rinse in fresh), and drinking. I got about a month out of the tank most times.
I got pretty inventive about collecting water but if it doesn't rain, all the tricks won't do much for you. I've been to islands where the water was either not available or too expensive for my cruising budget
Watermakers are expensive to buy, install, maintain, and use. However, it seems to me that a small unit in the 40-80gpd/160-320Lpd range is a viable 12/24VDC option. The biggest problem is the cost - it can easily reach USD4000 and may take a long time to recover the expense.
If I were to cruise
the more settled areas, then the watermaker might not be needed, but for long ocean crossings or locations were civilization is a thousand miles away, you don't have much choice. And as others have offered, water rationing is no way to see the world.