A well-designed water-making system makes life onboard more enjoyable. While conservation is exemplary, having to constantly monitor water usage can be stressful. Many cruisers love a long shower at a marina, but onboard Coco, we enjoy daily showers (or more, as needed) plus the washing machine. Of all the pros and cons of full time cruising, water does not have to be a limitation when your catamaran is set up well, keeping you independent from expensive marina habits. The saying goes: Go cruising, not camping.
Watermakers (marine desalination systems) use high-pressure pumps to drive seawater through reverse osmosis membranes and produce fresh water. This process is energy-intensive, so how you power a watermaker directly affects its output and efficiency. Below, we compare common power options – 12V DC units, inverter-driven AC units (110V/220V), generator/engine-powered systems, and solar-powered setups – focusing on their energy requirements and water production. On Coco, I’ve upgraded to a watermaker that can be powered by both solar and a generator, providing great redundancy in case the generator fails. But more on that later.
12V DC Watermakers
12V watermakers run on a boat’s DC electrical system and are known for their low power draw. They typically consume only a few amps, making them suitable for battery and solar setups. A common 12V watermaker might use around 8-10A (~100-120W) to produce roughly 1.5-3 gallons per hour. Thanks to such modest consumption, small DC units can run for extended periods on batteries or solar panels alone. This makes 12V systems ideal for smaller boats like monohulls..... cough cough or cruisers living off renewable energy.
However, the trade-off is lower water output. DC watermakers generally produce less water per hour than larger AC or engine-driven units. Many 12V models yield around 5–10 gallons per hour. To meet daily water needs, you’ll likely run a 12V watermaker for several hours a day. The good news is that this slower, steady output can often be managed entirely from renewable power—especially on catamarans, which have more space for solar panels than monohulls.
One key consideration is generator efficiency. If you are running the generator to charge batteries while using a 12V watermaker, you are also reducing the charge rate going into the batteries. This means you are not maximizing generator run time. I think 12V watermakers need to be ultra-efficient models, which tend to be expensive and require a frugal lifestyle. If you already have a generator and enjoy air conditioning, then an AC 110V or 220V watermaker is often likely a better option.
Solar Inverter-Powered Watermakers (110V/220V AC)
Inverter-powered watermakers are AC desalination units (typically 110V or 220V) run from a battery bank via a power inverter. These systems can produce significantly more water per hour than small DC units. AC watermakers often have larger pumps and multiple membranes – for example, a single-membrane 110/220V unit might consume about 1,000W and produce ~20 gallons of water per hour. This higher output means you only need to run the unit for a short time to make plenty of water.
The challenge is providing enough electrical power. Running a 1kW (or more) watermaker via an inverter puts a heavy load on the batteries. In practice, this setup requires an 800Ah+ lithium phosphate battery bank, either a high-output alternator on the engine or a large 2000W+ solar array, and a sizable inverter with adequate surge capacity for pump start-up. Boaters using this setup often run the watermaker when they can simultaneously charge the batteries or on a sunny day (for example, while motoring or using a generator).
On Coco, I can often make 150L in 1.5 hours from my solar-battery-inverter setup on a sunny day. However, if it's cloudy, then the generator is my go-to. Since we live at anchor most of the time and rarely use the main engines, installing larger alternators would not be an effective solution for us—our generator remains an essential part of the system.
Generator-Powered Watermakers
Generator-powered watermakers refer to systems that rely on a combustion engine for power – either an onboard genset producing AC electricity or a direct-engine-driven pump. These are common on larger boats and offshore yachts that need high water output and have the power capacity to support it. The defining feature is high water production: because a generator or engine can supply ample power, these watermakers can use bigger pumps and multiple RO membranes to crank out fresh water quickly. Many generator-driven units produce 20-60+ gallons per hour.
The efficiency and use case of generator-powered systems differ from the low-power units. If you already run a diesel generator daily (for charging house bank or air conditioning), diverting some of its capacity to make water is very efficient. Many cruisers schedule watermaking for times when the generator is on, effectively getting “free” water since the generator would be running anyway. The downside is the complexity and noise: installing a large watermaker or an engine-driven pump requires additional maintenance and fuel consumption. However, for off-grid living and larger yachts, this remains the most practical option for large-scale water production.
Solar-Powered Watermakers
The idea of a solar-powered watermaker is appealing: use the sun’s energy to desalinate water, eliminating fuel or noise. In practice, running a watermaker purely from solar panels has limitations. Most watermakers require steady voltage and substantial current, so you need batteries as a buffer to ensure the pump sees stable power.
A smaller DC unit drawing under ~10A (120W) can realistically be run from a modest solar array in good sun. For example, a 500W solar array could support a small 12V watermaker for a few hours a day. However, solar output fluctuates with clouds and shading, which can stall or shut down a watermaker if there is no battery storage. Because of this, most boaters use solar to supplement battery reserves rather than directly powering a watermaker. The key is having excess solar capacity beyond your baseline electrical loads, ensuring reliable water production even in varying sun conditions.
Trade-Offs and Considerations
Choosing how to power your watermaker is about balancing energy resources and water needs:
If you prioritize energy efficiency and quiet operation, a 12V DC watermaker is attractive – it sips power and can run off solar/wind, but you must run it longer to meet demand.
If you need more water faster but don’t want a separate generator, you need large solar arrays (2000W+) and an inverter-powered (battery-supplied AC) unit, which gives you big output at the cost of heavy battery usage and system complexity.
For maximum water production, generator or engine-driven systems deliver high volumes in short bursts, suitable for large crews or vessels – though you’ll burn fuel and handle more maintenance in return.
Solar can augment any of the above, effectively providing free energy for watermaking, but a purely solar-reliant setup needs larger inverters, ample solar panel capacity, and sunny weather to be viable.
A hybrid approach (like mine) offers the best of both worlds: I have a large solar array and both an inverter-powered and generator-powered 110V watermaker for redundancy, plus a smaller 12V semi-installed portable watermaker onboard.
References
My six years full time cruising experince
Manufacturer specifications for 12V and AC watermakers
Cruiser reports on energy efficiency and solar-powered watermakers
Expert recommendations for generator-driven systems
Real-world case studies from long-term liveaboard sailors
Every vessel has a unique power profile, so consider your daily water consumption, whether you regularly run an engine or generator, and how much battery/solar capacity you have. With the right setup, you can enjoy a consistent supply of fresh water on board. Go cruising not camping folks!!!
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