Straight answers.
The questions that come before you know what to shop for. Each one is answered in a sentence, with the figures computed from the 35 systems in our table rather than repeated from a brochure — and where the data cannot answer, the page says so instead of guessing.
How many watts does a marine watermaker use?Between 108 W and 2,800 W across the 30 systems we rank, with a median of 1,250 W. Watts on their own tell you almost nothing useful, though — a big pump that runs for twenty minutes can cost less energy than a small one running for three hours.108 W lowest draw1,250 W median2,800 W highestHow many amps does a watermaker draw?It depends entirely on the voltage, because amps are just watts divided by volts. The 18 DC systems we rank draw from 9 to 104 amps at 12 V, and half that at 24 V for the same work.9–104 A at 12 volts5–52 A at 24 volts31–164 Ah a day's waterHow much power does a 12 V watermaker use?The 12 twelve-volt systems we rank draw 108–700 W while running. For 100 litres a day that is between 31 and 106 amp-hours out of the bank.108–700 W running draw367–1,270 Wh energy per day92–318 W solar to matchHow long does a watermaker take to make 100 litres?Between 0.5 and 5.0 hours, depending on the system. 100 litres is roughly what 4 people use in a day at 25 litres each.0.5 h fastest5.0 h slowest1.5 h typicalHow much solar do I need to run a watermaker?Somewhere between 92 W and 493 W of panel to make 100 litres a day — a spread of more than 5× that comes down to which system you buy, not how much sun you get.92 W leanest system493 W thirstiest1,600 Wh the assumptionHow much battery do I need for a watermaker?For 100 litres a day, between 31 Ah and 164 Ah at 12 volts. Because you should not routinely take a bank below about 50%, that implies roughly 62–328 Ah of nominal capacity set aside for the watermaker alone.31–164 Ah drawn per day62–328 Ah nominal bank15–82 Ah at 24 voltsCan a watermaker run on solar alone?Yes — but the system decides it, not the sunshine. 6 of the 30 rated systems make 100 litres inside 500 Wh, which is comfortable on a modest array. 11 land between 500 and 1,000 Wh — most of a 400 W panel's entire clear day. The other 13 are not realistic on solar alone.6 systems comfortable11 systems a stretch13 systems not realisticCan I run a watermaker off an inverter?Sometimes — 10 of the 12 mains systems we rank draw under 2,000 W while running, which a large inverter can carry. But running draw is not the whole story: a high-pressure pump asks for a surge at startup that a sine-wave inverter has to absorb.10 of 12 under 2,000 w2,800 W highest ac draw18 DC systems the alternativeWhat size watermaker do I need for 4 people?Plan on about 100 litres a day — 4 people at 25 litres each, which is a cruising rate rather than a marina one. Almost anything in the table will make that; the question is how long it takes and what it costs in energy.100 L daily target0.5–5.0 h run time367–1,969 Wh energy costHow much does it cost to run a watermaker?In energy: between 669 and 3,593 kWh over five years of daily use, depending on the system. In dollars: we do not publish a figure, because what a kilowatt-hour costs you depends on whether it comes from panels you already own or diesel through a genset.669 kWh five years, leanest3,593 kWh five years, thirstiest2,924 kWh the differenceHow much water does a boat crew use per day?We plan on 25 litres per person per day for a cruising crew, and between 15 and 50 depending on the kind of boat and how it is used. That is a planning figure, not a measurement — the only number that matters is your own, and it is easy to get.25 L our default15 L frugal end35–50 L charter endHow many litres per hour do I need from a watermaker?Divide your daily need by the hours you actually want to run it. For a crew of 4 needing 100 litres and a comfortable one-to-two-hour run, that is 50–100 litres an hour — which is the middle of the market, not the top of it.100 L/hr one-hour run50 L/hr two-hour run20–222 L/hr in the table
Why these are short. A guide argues a case; an answer answers, states its assumption and points at the page that goes deeper. All the figures come from the same dataset as the comparison table, derived at build time, so they cannot drift from it. The guides are where the reasoning lives.