Are watermakers worth it?

The three questions that decide it

1. How many nights a year are you away from a tap? Not away from the marina — away from water. A boat that fills up every second weekend does not need one. A boat that anchors out for weeks at a time does.
2. How much water do your tanks hold? Tankage is the cheap alternative and it should always be considered first. If another 200 litres of tank solves your problem for a few hundred dollars, it is the better buy.
3. Where does your power come from? If the engine or a genset runs daily anyway, almost any system works. If you are on solar, the choice narrows sharply and the premium for an efficient system stops being optional.

What it actually costs to say yes

Four separate costs, and people usually only budget the first. The unit; the installation, which is often a substantial fraction of the unit price and depends entirely on the boat; the energy, every day, forever; and the maintenance habit — prefilters, flushing, pickling before layup, an annual service.

The fourth is the one that sinks systems. A watermaker that is not flushed and not pickled will not survive a season of sitting, and a membrane killed that way is a bill and a delay in a place where neither is convenient.

Those figures are the daily cost of saying yes. Multiply the watt-hours per litre by your real daily litres and you have the number that either fits inside your power budget or does not.

When it is clearly worth it

• You live aboard, or cruise for months. The jerry-can arithmetic stops working quickly and the freedom is the whole point of the boat.
• You cruise somewhere water is scarce, expensive or suspect. Much of northern Australia and most of the Pacific qualifies.
• You charter, or carry guests who do not ration. Consumption doubles and a water-limited trip is a refund conversation.
• Your boat already has the power. If a genset runs every evening anyway, the marginal cost of water is close to nothing.

When it is probably not

• Weekend and coastal sailing with marina access. You are buying a maintenance obligation to solve a problem you do not have.
• A boat that sits unused for long stretches. Idle systems are the ones that die; if it will not be run at least monthly, factor pickling into every departure.
• No electrical headroom and no appetite to add any. An undersized power system does not become adequate because you wanted it to.
• The budget only covers the unit. An installation quoted after the fact is where projects stall.