Estimating 8 guests and 3 crew, the 1,000-liter tank would require a water-maker.  Water makers are very efficient, however also some bigger loads say 50 liters per hour. So you need ~ 0.250 kWh for a 10-hour run ~ 2.5 kWh to make 500 liters.
Exactly — a water maker of 100 liter/ hour is what we would usually propose to our customers