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How does a water maker work?

The convenience of making your own drinkable water while cruising is priceless.  This was our number one requirement when we decided to travel around the world on our sailboat.

The first question was, should we get an AC or DC water maker?

Traditional AC water makers use a lot of energy because they require a feed pump and then a high pressure pump capable of producing a pressure of 600/800 psi to push water through the membrane.

Membranes have a microscopic pore structure large enough to allow water molecules to pass through it, but small enough to block salt, bacteria, etc.

Only a small percentage of the salt water (10/13%) is converted to fresh water: The rest is discharged overboard.

Because we decided not to have a genset, we had to get a DC low consumption water maker.  At the time, there were (and still are) only 3 low energy water makers in the world:

  1. Spectra (all models)

  2. HRO (Seafari Escape)

  3. Sea Recovery (Ultra Whisper)

Spectra is now owned by Katadyn and it’s based in Petaluma, California (close to where we used to live).

HRO and Sea Recovery are both owned by Parker Hannifin.

The technology, energy consumption, capacity and pricing are similar.  All offer similar options, but Spectra has much more experience and real world testing then HRO and Sea Recovery.

We found a good deal in South Africa, so we went for the Spectra Newport 400 water maker.

This water maker system can produce 70 liters (18 US gallons) of fresh water per hour using only 4 watts per liter (or 18 watts per US gallon)!

Spectra Newport 400

The genius idea behind this water maker is a unique “pressure intensifier system” called Clark Pump, developed by Spectra in 1997.

How does the Clark Pump work? The Clark Pump is nothing more than a pressure intensifier. It contains two opposing cylinders and pistons on a single rod.

Sea water goes through a small low pressure pump (feed pump) that uses very low energy because it only has to raise the water pressure to about 100 psi.

Then the pressurized water is injected in one of two opposed cylinders, each containing a piston connected by a common road.

The water entering the first cylinder moves both pistons.

The water into the second cylinder is injected into the membrane at a pressure of about 800 psi, and from there in the backside of the piston in the second cylinder.

When the piston reaches the top of the cylinder, the pump output is directed to the second cylinder, driving the pistons back the other way.

The discharge from the membrane is directed to the backside of the piston in the first cylinder.

Practically, the Clark Pump allows to reuse some of the brine coming out of the membrane feeding it to the back side of one of the pistons.

Pressurization is almost continuous. There is no energy wasting “back stroke” like in other systems and no need for gears or crank shafts that need oil and servicing.

All moving parts are made of non-corrosive material.

It seems complicated to explain with words, so here is a nice animation showing how it works:


Filtration consist of a raw water strainer, one 5 micron and one 20 micron pleated filters.  Filter supplied by the water maker manufacturer can be unreasonable expensive. However, there may be important details that influence their efficacy and life expectancy.  Third party filters may not fit properly and could damage pumps and membranes, so it’s better to buy the recommended ones.


Membranes are produced worldwide by only a handful of manufacturers. Most membranes in the marine industry are manufactured by FlimTec, a subsidiary of Dow Chemical.

If a membrane is left unused for more than a week, it will be fouled by bacteria.  This is why it’s important to flush the system periodically.  Typically, the water used for flushing is between 18/25 liters (5/7 US gallons) and it’s drawn from the boat’s water tank.  The Spectra water-maker has an automated flashing system, whereas in some bare-bone systems flushing needs to be done manually.

On average, membranes need cleaning once every 2 years and the average membrane life is 5 years.  Cleaning membranes is hard on them, and something of a crapshoot, so it’s better to replace them.


Z-ion is a Spectra proprietary system.  When a water maker is flushed with fresh water, small amounts of bacteria and microbes remain in the system.  As they grow, they consume the oxygen in the water and start to decompose.  They become anaerobic, start producing hydrogen sulfide (hence the rotten egg smell) and turn filters black, shortening their life.

The Z-Ion system is activated during the fresh water flush and produces silver ions that flood the entire system.  Silver is a disinfectant that eliminates the microbes and bacteria that cause biofouling of the filters and membranes.

With the Z-Ion you don’t have to flush more than once a month.

What went wrong so far

So far we have been quite happy with our Spectra.  It failed us only once, during the south Atlantic ocean crossing.  One of the cylinders developed a crack in the thread at the end cap.  I made a video out of the repair:


As I said in the beginning there are only a handful of companies making low energy water makers and their features and pricing are similar.

The key choice is whether or not to use a low energy system.  If your boat has a genset so that energy is not an issue, and you have a large family with high water needs, perhaps a traditional AC water maker is better.  That’s why most charter boats have AC water makers.

When comparing traditional water makers you need to look at:

  1. Degree of filtration of source water

  2. Quality of the boost pump

  3. Quality of the instrumentation (salinity sampling, automated flushing etc)

  4. Cost of filters and other parts needed for routine maintenance

For us having a low energy water maker was paramount.  And so far with the exception of the incident described in the video above, we have been pretty happy.

If you won an HRO or Sea Recovery, we would love to hear about your experience with them.  Please leave us a comment below.

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