Which watermaker is cheapest to run?

The Schenker Zen 30, at 3.7 watt-hours per litre. Making 100 litres a day it draws 367 Wh, which is roughly 92 watts of solar. The dearest to run in the table, the Rainman Modular AC 70L at 19.7 Wh/L, needs 1,969 Wh for the same water.

Why rank by energy rather than by dollars?

Because the dollar figure would be invented. What a kilowatt-hour costs you depends on whether it comes from panels you already own, a genset burning diesel at whatever it costs this month, or a marina pedestal. Watt-hours per litre is a published-spec derivation — rated draw divided by rated output — and it is identical for every reader.

Does a bigger watermaker cost more to run?

Not per litre. Output and efficiency are separate: the ranking above mixes 14 systems over 100 L/h in among much smaller ones. A high-output unit makes the day's water in less time at the same watt-hours per litre — often better for the batteries, because the draw lands in a shorter window you can aim at the middle of the day.

How is the solar figure worked out?

Watt-hours a day divided by 1600 Wh, the rough yield of a 400 W panel on a clear day, then multiplied back up to watts of array. It is a planning figure for comparison between rows, not a specification for your boat — real yield depends on latitude, season, shading and how flat the panels lie.

Running cost · updated 5 September 2026

The cheapest watermakers to run.

A watermaker is bought once and run for a decade. This page ranks all 30 rated systems by the second number: the energy each one needs to put water in your tank, what that adds up to over five years, and how much solar it implies. The purchase price is in the last column, where it belongs.

Cheapest to run3.7 Wh/LSchenker Zen 30

Dearest to run19.7 Wh/L5.4× the energy for the same water

Five-year spread2,924 kWhdifference at 100 L a day, best to worst

The scenario. 4 aboard at 25 litres each, 100 litres a day, every day for five years. Change the crew and every figure scales with it — the ordering does not.

System	Wh / L	Wh a day	5 years	Solar to feed it	Price
1 Schenker Zen 30	3.7	367	669 kWh	92 W	$6,300
2 Schenker Zen 100	4.0	400	730 kWh	100 W	$9,600
3 Spectra Ventura 150 Deluxe	4.5	450	821 kWh	113 W	$6,000
4 Spectra Ventura 150 Connect	4.5	450	821 kWh	113 W	$7,400
5 Spectra Newport 400C	4.5	450	821 kWh	113 W	$14,500
6 Schenker Zen 50	4.8	480	876 kWh	120 W	$7,800
7 Dessalator D100 DUOreported	7.0	700	1,278 kWh	175 W	—
8 Dessalator D60 Freedomreported	9.2	917	1,673 kWh	230 W	—
9 Dessalator D60 DUOreported	9.2	917	1,673 kWh	230 W	—
10 Rainman Portable AC 140L	9.8	984	1,796 kWh	247 W	$5,329
11 Rainman Portable 48VDC 140L	9.8	984	1,796 kWh	247 W	$6,240
12 Rainman Modular AC 140L	9.8	984	1,796 kWh	247 W	$5,460
13 Rainman Frame AC 140L, auto	9.8	984	1,796 kWh	247 W	$11,168
14 Rainman Frame AC 140L, manual	9.8	984	1,796 kWh	247 W	$7,685
15 Rainman Frame 48VDC 140L, auto	9.8	984	1,796 kWh	247 W	$12,115
16 Rainman Frame 48VDC 140L, manual	9.8	984	1,796 kWh	247 W	$8,666
17 LEDI Scout SW20reported	10.0	1,000	1,825 kWh	250 W	—
18 Rainman Modular 48VDC 140L	10.4	1,042	1,901 kWh	261 W	$6,421
19 Rainman Portable 24VDC 55L	11.3	1,132	2,066 kWh	284 W	$4,898
20 Rainman Modular 24VDC 55L	11.3	1,132	2,066 kWh	284 W	$5,053
21 Rainman Frame AC 240L Torrent, auto	12.6	1,261	2,302 kWh	316 W	$15,089
22 Rainman Frame AC 240L Torrent, manual	12.6	1,261	2,302 kWh	316 W	$12,089
23 Rainman Portable 12VDC 34L	12.7	1,270	2,317 kWh	318 W	$4,898
24 Rainman Modular 12VDC 34L	12.7	1,270	2,317 kWh	318 W	$5,053
25 Rainman Frame AC 100L, auto	13.9	1,389	2,535 kWh	348 W	$12,131
26 Rainman Frame AC 100L, manual	13.9	1,389	2,535 kWh	348 W	$8,642
27 Rainman Portable AC 75L	18.2	1,825	3,330 kWh	457 W	$4,402
28 Rainman Modular AC 75L	18.2	1,825	3,330 kWh	457 W	$4,522
29 Rainman Portable AC 70L	19.7	1,969	3,593 kWh	493 W	$5,296
30 Rainman Modular AC 70L	19.7	1,969	3,593 kWh	493 W	$5,299

What this page does not count

Consumables

Prefilters, membranes and chemicals are a real running cost and no manufacturer or dealer publishes them consistently. Rather than guess, we leave them out and say so. They scale with hours run, which makes an efficient system cheaper here too.

Servicing

An annual service is labour plus parts, and the rate depends on where you are and whether the technician comes to the boat. The servicing directory lists who does it; the questions there are what turn a vague number into a quote.

The cost of the energy

We do not convert watt-hours into dollars, because the rate is yours, not ours. Solar you already have is near free at the margin; diesel through a genset is not. The energy column is the honest common denominator.

Installation

A one-off, not a running cost, but often a large fraction of the purchase price and entirely dependent on the boat. Get it quoted separately from the unit so the two are comparable across suppliers.

Run it against your own boat

Your crew, your bank and your daily solar surplus decide which of these you can actually feed.

Open the calculator

Common questions

Which watermaker is cheapest to run?: The Schenker Zen 30, at 3.7 watt-hours per litre. Making 100 litres a day it draws 367 Wh, which is roughly 92 watts of solar. The dearest to run in the table, the Rainman Modular AC 70L at 19.7 Wh/L, needs 1,969 Wh for the same water.
Why rank by energy rather than by dollars?: Because the dollar figure would be invented. What a kilowatt-hour costs you depends on whether it comes from panels you already own, a genset burning diesel at whatever it costs this month, or a marina pedestal. Watt-hours per litre is a published-spec derivation — rated draw divided by rated output — and it is identical for every reader.
Does a bigger watermaker cost more to run?: Not per litre. Output and efficiency are separate: the ranking above mixes 14 systems over 100 L/h in among much smaller ones. A high-output unit makes the day's water in less time at the same watt-hours per litre — often better for the batteries, because the draw lands in a shorter window you can aim at the middle of the day.
How is the solar figure worked out?: Watt-hours a day divided by 1600 Wh, the rough yield of a 400 W panel on a clear day, then multiplied back up to watts of array. It is a planning figure for comparison between rows, not a specification for your boat — real yield depends on latitude, season, shading and how flat the panels lie.

How these numbers are made. Watt-hours per litre is the manufacturer’s rated draw divided by its rated output, never hand-entered. 30 of the 35 systems in the table publish both figures and appear here; the rest do not and are excluded rather than estimated. Rows marked reported are manufacturer-published and corroborated but not yet read page-in-hand, and are excluded from the headline best and worst above. Methodology · full table · by price.