Demystifying the Water Maker

Although Watts Up Marine Services focuses primarily on electrical, air conditioning/heating, refrigeration and electronic navigation systems, I get a lot of questions from folks about water makers. In a ‘former life,’ I worked with filtration and RO water systems that are associated with giant cooling towers in large buildings, power plants and data centers, which simplified the concept for me.  There seems to be some confusion around how water makers work, so I thought I’d take the opportunity through my latest water maker installation project to demystify them for my readers.

Reverse Osmosis (RO) Water Makers - How do they work?

Reverse osmosis is the process of forcing filtered sea water through a membrane at a very high pressure – about 800 pounds per square inch – which removes salt ions and other impurities, retains that solute on one side of the membrane and collects fresh water on the other side of the membrane. The membrane filters out most of the salt as well as bacteria, viruses, and other contaminants.   Further filtration of the fresh water occurs only to improve the taste and to adjust the pH.

I am installing a water maker on a 52-foot power boat that will be based in the Bahamas at a private island where there is no fresh water available, so the ability to take sea water and turn it into fresh water for showering, drinking and cooking serves a critical function. This Sea Recovery, Aqua Matic water maker is able to provide 29 gallons of fresh water per hour: 700 gallons per day.  Salt rejection for these units averages 99.4%.  That's probably better quality water than what comes out of our taps at home!

The keys to its reliability are the proper planning, initial installation and the correct regular maintenance.  There are several things you must take into account:

• How much fresh water will you need per day? Per hour?  How much water you need will determine the amount of power you need to supply your water maker.
• How much power consumption you can provide, and what type of power -- 12/24v D/C or 115/230v A/C?  The more water you need, the more power it will require.  If a generator is available, this issue becomes much easier to resolve. But if you are limited in the power you can supply, you may need to rethink your water consumption requirements.
• Where in the world will you be, and can you get spare parts?  Do you need a system with an absolute minimum of proprietary parts on the machine, so no matter where in the world you go, the machine can be serviced and repaired using parts and supplies that can be sourced easily? Something to be considered if you want to romp in the less-developed parts of the world.
• How much automation do you require?  Do you need a fully automatic system that will flush the membrane on a regular basis or make water as needed or do you just need one that will make fresh water?  You should weigh your willingness/ability to perform manual functions before choosing your system.
• How much room do you have for a water maker?  There are two types of water maker systems: compact or modular.  Compact systems have most of the major components enclosed within one frame.  The only remaining items that would require mounting somewhere in the boat would be the booster pump, which supplies raw water to the compact water maker, and some pre-filters.  If you have no room to mount a compact system, you may opt to go modular, which is comprised of individual parts that can be installed in different parts of the boat when space is an issue.
• How much can you spend?  The amount of water you will require and the automation you select will be reflected in the investment you make.  Don't always purchase the unit that is most cost effective with the initial purchase, the cost in maintenance and consumables might surprise you later.

Once you select a system, you then have to consider installation.  Here are the major points:

• Where to install the raw water intake?  It must be well below the waterline on the hull, away from any turbulence while underway. Air bubbles caused by turbulence can be pulled into the intake and “explode,” -- cause cavitation inside the high pressure pump. This can deteriorate the metal surfaces inside the pump and cause pump failure.
• How is your boat's hull constructed? When installing the intake, the number one thing to avoid is allowing sea water to seep into the many layers of your hull.  If your hull is fiberglass with a foam or balsa core, your intake installation must include steps to seal the area around the intake to ensure that if the thru-hull someday begins to leak, it won’t saturate the material sandwiched between your fiberglass layers, causing major hull damage.
• Where do you fill your fresh water tank? You will want to consider where your tank fill is located so you can properly plumb it to fill with fresh water.
• Where does your water tank vent? Some boats' water tanks vent into the bilge, so if your water maker overfills the tank, you fill your bilge. An automatic shut-off may be necessary.
• Where do you drain the waste?  The brine waste that is rejected by the membrane has to go somewhere! Directly overboard is best, so figure that you'll have to plumb some sort of overboard drain.

My next blog post will describe, step by step, the installation of the Sea Recovery water maker, with pictures, so I hope you check back in for more information.  Meanwhile, feel free to post any of your questions about water makers and I’ll be happy to respond. See you soon!