A watermaker is a reverse-osmosis (RO) system that turns seawater or brackish water into potable fresh water by forcing it, under high pressure, through a semi-permeable membrane that holds back dissolved salts and most contaminants. For a boat on passage or a vehicle far from a reliable tap, a watermaker converts an effectively unlimited resource into one of the few consumables you would otherwise have to carry. The trade-off is that fresh water is produced at the cost of energy, so the right system is the one matched to both your demand and your power budget.
How reverse osmosis works
Osmosis is the natural tendency of water to move across a membrane from a less salty to a saltier solution. Reverse osmosis does the opposite: a high-pressure pump pushes salty feed water against the membrane hard enough to overcome that tendency, so pure water passes through and the salt is left behind. Seawater needs substantial pressure to cross the membrane, which is why the high-pressure pump is the heart of the system and the largest single energy consumer.
The water that comes through the membrane is the permeate (your product water). The salty stream that does not pass through is the brine or concentrate, and it is discharged overboard or to waste. A typical install also includes pre-filters to protect the membrane from sediment and silt, and many systems offer a post-treatment or flush stage. Membranes dislike sitting wet and idle, so a fresh-water flush after each use is one of the simplest ways to extend their life.
Where the energy goes, and the Clark Pump
Conventional watermakers waste the pressure energy still held in the brine, dumping it overboard. Energy-recovery designs reclaim it. The best-known example in the marine world is the Clark Pump used in Spectra Watermakers systems: a pressure-intensifier that uses the energy in the outgoing brine to help pressurise the incoming feed water. The practical result is that an energy-recovery system can produce a given quantity of fresh water for considerably less electrical power than a comparable conventional unit.
For a yacht running off a battery bank, or an overland vehicle on solar, that efficiency is the whole point. Lower draw means you can make water from house batteries without running the engine or a generator, and it eases the load on the rest of the energy system — the same system PowerSol supports with Victron Energy charging and monitoring and Pylontech or similar LFP storage.
Sizing by crew and usage
There is no single correct watermaker; there is the one that meets your daily demand within your power and space constraints. Rather than chase a headline output figure, work through your own numbers qualitatively.
- Crew and trip length. More people and longer passages mean higher demand. Be honest about washing, cooking and the occasional deck rinse, not just drinking water.
- How you will run it. A small unit run for several hours daily suits a vessel with steady power. A higher-output unit run briefly suits one that wants to make a day’s water in a single window — for example while the engine or generator is already running.
- Power source. Match the high-pressure pump’s draw to what your batteries, solar and charging can comfortably sustain. This is where energy recovery earns its place.
- Space and mounting. Modular systems let you separate the pump, membrane and controls to fit awkward lockers. Compact all-in-one units are simpler but need a single home.
- Water quality and pre-filtration. Murky harbours, river mouths and silty overland sources demand more pre-filtration and more diligent maintenance.
A quick comparison
| Consideration | Smaller, run-longer | Larger, run-shorter |
|---|---|---|
| Daily run time | Several hours | A short window |
| Instantaneous power draw | Lower | Higher |
| Best paired with | Steady solar or battery bank | Engine or generator already running |
| Tank turnover | Gradual | Bulk, less often |
Living with a watermaker
Three habits decide how long a membrane lasts. Pre-filter discipline — change cartridges before they choke the pump. Regular use or proper preservation — run the system often, fresh-water flush after each session, and chemically pickle it for long lay-ups. Clean feed water — avoid making water in marinas, anchorages with poor flushing, or anywhere with fuel sheen or heavy sediment.
Test product-water quality periodically. A handheld TDS meter is a cheap way to confirm the membrane is still rejecting salt properly; a rising reading is your early warning that service is due.
The bottom line
A watermaker removes the single biggest logistical limit on time away from shore. Choose by demand and power budget rather than peak output, favour an energy-recovery design such as a Spectra Clark Pump system where battery-only operation matters, and build the rest of the energy and filtration chain to suit. PowerSol can help specify a watermaker alongside the Victron Energy and LFP infrastructure that powers it, so the whole system is sized to work together rather than as parts that happen to share a hull.