Every watermaker brochure gives you two numbers: output in litres per hour and draw in watts. Neither one tells you whether the system fits your boat. Divide the draw by the output and you get watt-hours per litre, which is exactly what your battery bank pays for every litre of fresh water. It is the spec that decides everything, and almost nobody prints it.
Across every rated system in the table, the spread runs from 3.7 Wh/L for the Schenker Zen 30 to 19.7 Wh/L for the Rainman Portable AC 70L. That is a five-fold difference between two products a cruiser would happily cross-shop, sitting invisibly inside the spec sheets.
Put it on a real boat. A family of four using 25 litres a head is 100 litres a day. At 3.7 Wh/L that is 370 Wh, roughly what a single 400 W panel makes on a fair Queensland morning. At 19.7 Wh/L it is 1,970 Wh, more than most 12 V house banks can spare without running the engine or a generator.
The whole market, ranked
| System | Power | Output L/hr | Draw W | Wh per litre | Price |
|---|---|---|---|---|---|
| Zen 30 Schenker | 12/24V DC | 30 | 110 | 3.7 | $6,300 |
| Zen 100 Schenker | 12/24/48V DC or AC | 100 | 400 | 4.0 | $9,600 |
| Ventura 150 Deluxe Spectra | 12/24V DC | 24 | 108 | 4.5 | $6,000 |
| Ventura 150 Connect Spectra | 12/24V DC | 24 | 108 | 4.5 | $7,400 |
| Newport 400C Spectra | 12/24/48V DC | 64 | 288 | 4.5 | $14,500 |
| Zen 50 Schenker | 12/24V DC | 50 | 240 | 4.8 | $7,800 |
| D100 DUO Dessalatorreported | 12/24V DC | 100 | 700 | 7.0 | on request |
| D60 Freedom Dessalatorreported | 12/24V DC | 60 | 550 | 9.2 | on request |
The pattern behind the numbers is the pump. Energy-recovery DC systems, Schenker's ERS and Spectra's Clark pump, cluster between 3.7 and 4.5 Wh/L. Conventional high-pressure-pump systems sit between 10 and 20. Neither camp is wrong. One buys efficiency, the other buys output and a lower purchase price. You just need to know which one you are buying before the dealer tells you.