40 Gallon an Hour Watermaker For Less Than $4,000 Part II

22 Jul

Here’s part 1 of the watermaker install for those of you who missed it.

The install resumed on the hook in Marsh Harbor, Bahamas. I had plenty of time to work on it after we arrived thanks to 30kt winds for over a week. The pump was installed on the mount and then bolted to the engine rails inline with the power takeoff pulley. After three trips to the store I finally got the correct sized belt. Ideally I would have liked to attach the mount directly to the engine. With my setup you have to be careful not to put to much tension on the belt as it will mess with the mounts and screw up the alignment of the engine and prop shaft. Lucky the setup works great with minimal belt tension and I’ve noticed no ill effects on the engine, shaft, mounts or cutlass bearing in 500 hours of operation since the install.

With the pump mounted and the pressure vessels installed in their space the project now turned into a plumbing and electrical tetris game. I built a control panel with two heavy duty switches and a fused terminal block for each circuit. The entire system is driven off a 15amp single circuit from the main panel. When looking at all the fancy computer controlled units out there I’m happy with my extremely simple two circuit system. One circuit controls the electromagnetic clutch and the other controls the boost pump that supplies the high pressure pump with a constant stream of clean seawater.

The plumping was the most labor intensive part of the project. With the pump by the engine, the pressure vessels forward and then the filter/boost pump setup still further forward it was quite an endeavor to run all the hose to connect everything up.

DIY watermaker valve assembly

I have a thing against putting holes in my boat. When I bought her, the boat had about 10 below the waterline and I removed all but 4. To supply the water maker I teed my wash down pump seacock as it was the correct size and conveniently located. We generally make water underway and never need the wash down pump when the watermaker is running.

DIY watermaker DIY watermaker control

After everything was connected and the circuits were tested, I started the contraption up for the first time. It was pretty exciting – I knew all the theory and that it was supposed to work, but seeing it output fresh water for the first time was amazing. To start the unit I first open the seacock (it stays shut when not in use do to the amount of plumping connected to it and the number of theoretical failure points) and turn on the booster pump circuit. Now I wait till the entire system fills up with water and all the air is purged. Next, the engine is started and set to an RPM of about 1400.  The high pressure pump circuit is turned on and the system continues to purge without any pressure. Once I am sure I got all the air out of the system I slowly increase the pressure and watch my sample hose and bucket. After the pressure climbs to about 400 psi I check all my high pressure plumbing. No leaks so far! Now I increase to 500 psi and start to see some green liquid come out of my product hose. This was the storage solution and after a few minutes it turned clear. After checking for leaks and checking the pump belt I increased the pressure to 850 psi and the product stream increased to that of a sink faucet. I let about 5 gallons run out and then dropped a glass under the product water hose, raised the glass to my lips and took a swig. Clean, cold, tasteless water! Unbelievable.

Since then we’ve made thousands of gallons of fresh water, taken hundreds of showers and even washed the boat down. Having an endless supply of fresh water that can be produced in a relatively short amount of time it is a luxury that Rachel and I feel was worth the cost and installation time. I enjoyed learning how the system worked and assembling it. I’m an expert on the system in our boat and can fix any part of it, even rebuilding the pump if needed. That’s a claim most with other proprietary systems cannot say. If I should need new membranes they are mass produced and only cost about $250 each, compare that with the cost of other manufactures membranes and the DIY watermaker will look even more attractive.

The downsides to the DIY watermaker are the size and amount of room it takes up. Given the amount of water it produces I’m ok with this tradeoff – we had the space on our boat. Another issue with this system is I think it scares some people. They want to press a button and have it produce water without manually operating the unit. This fact may lower the resale value if the boat was ever sold. I’m convinced however that since its well installed and comprised of quality components, to the right buyer it will actually be an advantage.

Let me know if you have any questions about the installation or the parts and I’d be happy to share further information.


This article was syndicated from Cruising – Beautiful Crazy Happiness


  1. Glenn Packer

    I would not worry over resale value. Ships systems are of very little value at resale time due to there uncertain history , maintenance record and needs or wants of the new owner. To someone buying your boat for weekend use a water mater has no value at all. I find your choice of a DYI system to be an excellent choice providing you with a robust useful system at rock bottom cost.

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