Watermaker, bigger tanks, or jerry cans?

What each one really costs

Where jerry cans stop working

Twenty litres weighs twenty kilograms and has to get from a tap, into a dinghy, alongside, and up onto a deck without going over the side. Two or three of those is an errand. Ten is a day, and it is the day you wanted to be sailing.

They remain the right answer for topping up before a passage, for emergency reserve, and for boats where the anchorages have a tap within a dinghy ride. Keep a couple aboard regardless of what else you do.

Where tankage stops working

Tankage is bounded by the boat. When the honest answer to “where would another tank go” is nowhere, or when the weight would sit in the wrong place, you have found the limit. A tank is also a fixed range: it decides in advance how long you can stay, and no amount of care extends it.

It is still the cheapest buffer you will ever buy, and it is what makes a watermaker practical rather than redundant — you make water when the sun is out and draw on the tank when it is not.

Where a watermaker earns it

One thing only: it converts a fixed range into an open-ended one. If the constraint on how you use the boat is how long the water lasts, nothing else removes that constraint. If the constraint is something else — time, weather, the crew's patience — a watermaker will not fix it, and you will have added a system to maintain for nothing.