Water Maker DIY - Part II

Today is the final post on the topic of reverse osmosis water maker systems.  In the previous post we discussed the systems needed to take water from the sea, pump it, filter it and then run it through the high pressure pump and RO membrane.  Today's topics will give more information on the things that are not usually seen: the things that keep everything running and doing what they are meant to do. 

Post RO

Automation/Controls

Automation is a convenience, but it is a convenience that I will not live without on the system that I would construct.  Yes, you could do everything manually, like changing valve positions, turning on pumps, and increasing or decreasing system pressures.  However, if you are going to have a water maker system that will last for many years to come, automation takes out some of the human error that is bound to occur.  


There are many different vendors supplying controls to run an RO water maker.  The determining factors are the amount of automation you want, the size of your water maker, the amount of power you have available and what you're willing to spend.  I am considering a Series 150 microprocessor controller made by R&D Specialties however there are numerous controllers available. Here is some information provided by HCTI:

Features:

•Economical compact package
•Liquid crystal display and multi-function keypad
•English or metric TDS and temperature values
•Visual and audible alarm, with alarm silence key
•Programmable time delays and set points
•Programmable flush mode
•Low pressure automatic reset
•NEMA 4X hinged enclosure
•Panel or frame mount
•Available with UL/CUL Listing

R&D Specialties, Series 150 RO Controller

Standard functions of the Series 150 controller are the monitoring and/or control of:
•RO high pressure pump motor
•Inlet solenoid valve
•Automatic flush solenoid valve
•Low feed pressure switch
•High pump pressure switch
•RO storage tank level switches (1 or 2)
•Permeate TDS/Conductivity
•Water temperature
•Pre-treat lockout
•Operating hours
•RO tank full override

 *TDS stands for Total Dissolved Solids 

Switch Inputs, Dry Contact:

• Pressure fault - low feed and/or high pump pressure

•Tank level high

•Tank level low

•Pickled treatment lockout

Relay Outputs:
•High pressure pump relay - 120/240V, 1 HP

•Inlet valve relay - 120/240V, 5 AMP

•Flush Valve relay - 120/240V, 5 AMP

•Relays supply same output voltage as board power (120 or 240V, VAC)

Valves/Water Control

I have seen numerous RO systems that have no automation and work very well, as long as the operator understands the system completely.  Knowing the water flow during each of the water making processes, start-up and fresh water flush can be difficult for someone that does not do this on a regular basis.   

In the system that I would design, complete automation is a requirement.  I want to be sure that anyone can operate the system even when I am not there to instruct.  Most good RO water maker controllers will have the inputs and outputs to control solenoid valves as needed.  The three way valves that will be used in this application will simply connect into the outputs on the controller.  Another function that would be handy, yet is not a must, is an automatic shut-off when the holding tanks are full.  Royce Industries makes an electronic level sensor that could be used to shut off the system when needed.  I know that I would often forget to monitor the water tank levels and it would be nice to know that the system is doing this for me.

Post Filtration

Post filtration such as carbon filters and pH neutralizers will simply help the flavor of the product water.  I feel it is a matter of preference rather than need.  In the system that I install, this will not be needed, yet could easily be installed at a later date if I so desire.  

UV Sterilizer

Ultraviolet Sterilizer

A U.V. sterilizer is recommended if the feed water (intake) is from a harbor, marina, or polluted source. The RO membrane rejects bacteria and viruses, however if biological migration occurs across the membrane, then the U.V. sterilizer will destroy 99.9 % of any biological intrusion in the product water.

Fresh Water Flush

Fresh water is required to flush or store the water maker.  Fresh water flush will greatly prolong the life of the reverse osmosis membrane elements by rinsing them with fresh water.  The fresh water flush will need to repeat itself every seven days.  By rinsing the water maker, salt water is displaced with fresh water within the RO system’s internal parts. This process will prevent corrosion of the internal parts and also reduce biological fouling of the membranes.

The fresh water used to flush the RO system is taken from the boat's pressurized fresh water system.  To ensure that chlorine does not enter the system, the pressurized water should go through a carbon filter first.  The carbon filter will remove any chlorine that might have entered the tanks when filling at the marina.

After the fresh water goes through the carbon filte,r it is a good idea to introduce it to the water maker at a “T” before or after the sediment filters.  If the fresh water is introduced before the sediment filters, it will offer additional protection to these filter cartridges.

According to one manufacturer of the RO membranes, membranes age as they sit unused. So delay the purchase of your membranes until after you finish installing the rest of the RO system and you are ready to use the system.

Pickling
The process of pickling, consists of adding a food preservative (sodium metabisulphite) to stop bacterial and fungal growth on the membranes and in the pressure vessel, is widely regarded as being effective for at least 3 months. I know of several RO systems on yachts that have been pickled for 1 year or more. One disadvantage to pickling is, the preservative leaves its mark on hoses (especially PVC), bronze fittings and stainless steel.  Given the option, I would prefer not to pickle the RO membranes but instead flush them frequently with unchlorinated fresh water.  The frequency of fresh water flush depends on ambient temperature: the warmer the temperatures, the more frequent a fresh water flush will be required.

Control automation is key to keeping the system clean and operational every time you will need it.  Many microprocessor controlled systems will give you the ability to program the frequency of fresh water flush.  Membranes can be pricy and forgetting to flush the membrane could result in added expense.  Water maker controllers can be a great insurance policy.

Ensuring that you have a properly functioning RO water system

Important things to DO: 

1. Change the cartridge filters regularly. 
2. Monitor the system and keep a log daily.
3. Run the system, as much as possible, on a continuous basis.
4. Pickle the system if you do not intend to operate for long periods.

Important things NOT to do:

1. Permit chlorine in the feed water.
2. Shut down the system for extended periods without pickling.
3. Close the throttle (pressure) valve completely.
4. Operate the system with insufficient feed flow.
5. Allow the membrane to become dry. 

Water Temperature - How does this affect the operation?

Temperature of the feed water can affect the water maker's ability or inability to make fresh water.  As the temperature of the feed water drops, so will the fresh water production.  As the temperature of the feed water increases, the fresh water production should also increase.  With this known, a decrease in feed water temperature can be compensated by increasing the feed pressure up to the maximum allowed by the membrane, pump and associated components.  Once the maximum pressure is reached, a further decreasing temperature causes the permeate flow to decrease and nothing more can be done.  Increasing temperature is compensated by lowering the feed pressure.

Seawater/brackish water operation-What might we change?

Feed water salinity can also affect the water maker’s ability and efficiency.  An increase in the feed water salinity can be compensated by increasing the feed pressure up to the maximum. If further pressure increase is not possible, than a lowered permeate flow and system recovery has to be accepted.  A lower feed water salinity, such as the brackish bay water, allows us to decrease the feed pressure and continue to receive the same product water flow.


Budget
Now for the most important information of this series, the cost!  Currently the costs for the major components are listed below, however there are additional costs for all the minor components that I have factored into my budget.  When looking at a good water maker system, the costs will be $7,000-$10,000 for a pre-constructed system that will produce more than 100-150 gallons in a day, I think I will easily be able to do better than that.  Here are the items that will put the biggest dent in your checkbook. 

• Low pressure feed pump     - $250
• High pressure RO pump      - $750
• High pressure pump motor - $250
• High pressure vessel            - $350
• RO membrane                      - $200
• RO Controller                       - Awaiting pricing information
  

So that's it in a nutshell (in three posts!). Water makers mystify a lot of people, but they are really very simple filtration systems once you wrap your brain around exactly how they work. Questions?  Hit me. I'll be happy to answer any questions you might have about your unique situation.

Yes, you CAN build your own water maker!

In my previous water maker posts, I described the process of installing a Sea Recovery water maker and briefly covered the components that make things work in this self-contained system. 

I want to make my own reverse osmosis (RO) system that would use components that could be found anywhere I might be cruising.  Most of the major parts of a system can be found at most local distributors or on the internet.  The challenge would be automating an off-the-shelf system. But if you understand the system and what it would require to operate, the cost savings you experience building your own water maker versus purchasing one might be worth it. 

An additional advantage is the ability to make a fully modular system.  On the sailboat that we own, our system has to be modular – we need to put each component in strategic areas to best use the available space.  Modularity also allows us to mount the high pressure pump and motor in a location that might be easier on our ears.

Let’s explore the information you need to take the plunge:

Reverse Osmosis 101

As I touched on in my previous post, RO is a separation process that uses high pressure to force a solvent through a membrane that retains the solute (solids, salt and impurities) on one side and allows the pure solvent (fresh, drinkable water) to pass to the other side.  In reverse osmosis, the idea is to use the membrane as an extremely fine filter to create drinkable water from salty water.

The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases, the membrane is designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions). This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 30-250 psi for fresh and brackish water, and 600-1000 psi for seawater.  Most water makers designed for yachts currently operate at around 820 psi.

RO is used to reduce dissolved solids from feed waters. Municipalities and industrial facilities use RO permeate as a consistently pure drinking water supply and to transform drinking water to high purity water for industrial use at microelectronics, food and beverage, power, pharmaceutical facilities, and can be used for removing bacteria and organic contaminants.  In the production of bottled mineral water, the water passes through a RO water processor to remove pollutants and microorganisms, including the some of the smallest microbes known as Achaea. 

Here is a further cut away diagram to help describe the RO membrane function:

In this diagram, the "Feed" is the high pressure output from the pump and the "Back feed" is the pressure that is built up behind the pressure adjustment valve that is installed in the brine outlet line.  This high pressure then allows the "Permeate" or fresh water to filter through the membrane while leaving the impurities to continue their flow to the brine outlet.   

Looking at the complete system:
There are many components that make the RO system work. Many are very simple items and easily found.  The rough diagram below shows the water flow through the system.

Water maker diagram

To make things easier, I will break these down into three categories, Pre-RO, RO and Post-RO (Before, During and After) and list each item in the sequence that they will be used.

Pre-RO Systems

Raw Water Supply Pump – drawing sea water into the system

In the system I want to build, the seawater will enter from the raw water thru-hull and go to the supply pump.  Be sure to include a seawater strainer just after the thru-hull, thus catching any debris that might damage the pump.  This pump will deliver an adequate amount of raw water to the system and maintain 45 psi pressure to the water maker.  This pump could be 12vdc, 24vdc, 115vac or 230vac depending on the type of system you would like to use on your boat.  In my case, I would use a commercial duty 12vdc rubber impeller pump because I would like to use it for multiple purposes:

• I will add a three-way valve before the pump, it could serve as an emergency bilge pump 
• I will put a three-way valve after the pump to use as a saltwater wash-down pump.   

Just following the pump, I will add a pressure switch that will control the pump and system pressure to the desired feed pressure.  A pressure sending unit will also alert the RO controller to a low feed pressure status and shut down the system for safety.

Jabsco pump

 

  Sediment Filters – the initial filtration

As the RO membrane is very sensitive, it’s important to filter out larger particles before the raw water is forced through the membrane. Therefore, the raw water pump will deliver the saltwater to a series of sediment filters.  I will use common cartridge water filters, the first filtering to 30 microns and the second to 5 microns.  These filters can be purchased online or at a supply store such as Grainger.

For convenience, I would add some simple pressure gauges before and after each filter housing so that I can compare the inlet and outlet pressures.  The comparison of each pressure will tell me if the filter element is starting to become clogged.

Sediment filters

Oil Separator – keeping petroleum out of the system

Petroleum is harmful to the RO membrane, so it’s extremely important to remove any petroleum products such as diesel, oil or gasoline from the raw water before it enters the water maker system (believe me, any water, anywhere, is full of petroleum).  Petroleum will destroy the RO membrane.

Oil/Water separation filter

RO Systems – the magic that turns salt water into fresh water.

High Pressure Pump/Motor

This pump/motor combination will supply the high pressure needed to "press" the water solution through the RO membrane.  The power needed to drive the high pressure pump is higher than most marine applications, so think carefully about how your boat is able to power it – either via DC or AC.  Most 12vdc high pressure pumps require about 26 amps to operate; 24vdc would need 13 amps.  This would require most boaters to run the engine while fresh water is being produced.  If a generator is available, the choice is simple, and AC is more practical. 

There are numerous pump/motor combinations that you can find by simply conducting a quick internet search.  I have researched a number of high pressure pumps and have chosen a direct drive Cat Pump model 2SF with a Baldor motor.  This pump should deliver 0.17 gallons per minute (GPM) or 10 gallons per hour (GPH), meaning I would have to run my system for one hour each day to produce the fresh water that I usually consume.  If I increase the pump size, I could produce more water in a shorter amount of time; it all comes down to power consumption and run time.  Soundproofing this component would be a serious consideration due to the noise that it can produce.

High Pressure Cat Pump

High Pressure Vessel – the home for your RO membrane

The high pressure pump feeds seawater to the high pressure vessel, which houses the RO membrane.  This vessel has three connections or ports: one inlet and two outlets.  As the seawater passes through the vessel through the inlet port, the membrane will then separate the fresh water and the remaining brine.  The fresh water will exit at the product water port (outlet 1) and the brine will be discharged overboard via the brine port (outlet 2).  

There will be a high pressure adjustment valve on the brine outlet (outlet 2), maintaining the correct system pressure needed to force the fresh water through the membrane.  A flow meter on both the brine outlet and the product water outlet will allow you to get a good comparison of flows.  This comparison will tell you how well the system is working and if the membrane is getting fouled.

I am selecting a high-pressure vessel from HCTI from California.  Select a vessel that will offer the correct flow and dimensions that allow generic RO membranes to be used.  Common diameters are 2.5", 4" and 8" while lengths come in 14", 21" and 40".  For most recreational boaters, one RO membrane will provide all the water they might need, provided the correct sizing has been met; however, vessel/membranes can be arranged in serial or parallel to produce more product water per day.

High Pressure Vessel

RO Membrane – the diva of your water maker system

The RO membrane is the key to a water maker’s success. It is also the item that needs the most attention before building your unit, during operation and maintenance after use. 

It’s important to choose a membrane size that gives the quantity of product water you need, and to fit inside the installed high-pressure vessel.  But as with all things on a boat, bigger means pricier - replacement membranes aren’t cheap.

RO Membranes

 

I repeat: membranes aren’t cheap. So here are some tips on maintaining the longevity and integrity of this component – before, during and after use:

• Usually, the first hour of product water from a new membrane must be discarded 
• Keep system pressures below maximum pressures, usually 1000 psi.
• Hydraulic shock can destroy the membrane. Slow changes in pressure must be gradually increased over a 30- 60-second time frame.  Control automation can mitigate this risk.
• Once water is added to the membrane, it must remain moist at all times. This means you have to use the water maker regularly, or pickle it (see last bullet).
• Avoid any sudden pressure changes to the high pressure vessel
• Fresh water flush is crucial to longevity of the membrane.  Pickling with chemical is needed for long periods without use.

I could go on and on about this topic however there is just not enough time in the day for me to continue writing and most likely for you to continue reading.  If you made it this far, congratulations!  Join me in the next blog post when I will be discussing

• Automation/Controls - the stuff that makes all the kids play nice together.
• Valves/Water Control
• Fresh Water Flush/Pickling

The RO system that is made "Do-it-yourself" style, can easily surpass the packaged systems that are currently sold.  Not only will you leave some money in your pocket but you will gain the knowledge to fix it yourself when the need presents itself.  

Water Maker Installation

Okay, a little insomnia motivated me to expand on that water maker 'demystification' post from a few days back!

As I explained, there are many different types and sizes of water makers on the market. Some are fully contained, and and others are semi-modular or fully modular components which you can install throughout your boat. 

   
They come in varying levels of automation - from simple manual operation to fully automatic. Some of the major items they all require are:

• A raw water intake hose from a thru-hull installed below the waterline and away from turbulence
• A low-pressure supply pump that delivers sea water to the pre-filters and then feeds the high-pressure pump
• Pre-filters
• Oil/water separator
• A high-pressure pump that will develop between 800-1000 PSI to the reverse osmosis membrane
• The membrane and filtration systems
• Wiring the water maker into your AC/DC electrical system
• Plumbing to deliver fresh water into your water tank
• A series of manual or automated valves to supply a fresh water flush to the system after each use.  This is a topic that we will discuss in greater detail within an upcoming post of this water maker series.

Here’s how that Sea Recovery install went:

• On this installation, the hull I was drilling into had a double core made of foam with a thick exterior and interior fiberglass layer and a thinner sandwiched layer as shown below.  The total hull thickness was approximately 2.25".

 

• We had to make certain that the exposed foam was completely water tight. Otherwise, water could easily seep within the core of the hull and cause serious damage to the boat. I drilled a hole that was larger than required by the 1" thru-hull, then removed about half an inch of foam material from the complete circumference of the hole.  A good rule to follow: Remove the same amount of core material as the diameter of the exterior flange of the thru-hull fitting.  The thru-hull flange will then clamp down upon a solid, water-tight base.

• We then filled the new hole completely with two-part epoxy and allowed it to cure.  This process will then give us a solid base that can be drilled and not allow seawater into the foam core even if the thru-hull should someday leak.

•  Now that the epoxy has cured and we have a solid base for the new thru-hull, we could then drill our 1" hole and properly install the thru-hull fitting.

• In the photo below, we have installed the thru-hull and backer plate on the interior of the hull.  The backer plate is a rigid disc made of wood, plastic, fiberglass, or other water-resistant material that is bonded to the inside of the hull at the location of a through hull penetration. The disc adds thickness and strength, and provides a solid platform through which the seacock flange can be mechanically fastened, effectively spreading the load exerted by the seacock over the increased area of the disc. 

• The photo below shows the other side of the thru-hull on the exterior.  Always ensure that the thru-hull and the seacock are made of the same material; NEVER mix polypropylene or marelon with bronze - you risk breaking the more fragile material as you tighten down the bronze fixture.   

        

• The next step is to install a supply pump that will move the raw seawater from the seacock to the pre-filters and then on to the water maker.  The plumbing is simple and should need no explanation, however one bit of advise I would give is to ensure that the base has some sort of vibration dampening device to reduce noise and potential wear and tear.  For this installation, I simply used some rubber feet on the base of the pump.  Running electrical to operate this pump would vary according to the water maker that you are installing and the automation that is provided.  Refer to the manufacturer of the water maker to determine the correct wiring and wire size.

• In order to provide longer life to the high pressure membrane, pre-filters are needed.  Pre-filters will remove debris that could damage the water maker. Some of these filters are:

• Oil/water separation filter
• Plankton filtration to filter out debris larger than 100 microns
• Multi-media filters to filter out debris larger than 5 - 30 microns
• Mount the water maker in a secure location while also keeping in mind that service accessibility is very important.  Mounting this unit required the removal of four rubber mounts, bolting them to the shelf and then re-installing them on the water maker.  In most cases, if the water maker is a compact design (one that packages most of the major components into an enclosure) servicing it will often be difficult due to space constraints.  Modular units allow you to install the pumps and membranes in areas with easier access.
• Plumbing to the water maker is as easy as running the water hose from the last pre-filter to the inlet of the water maker or high pressure pump.
• Electrical to the water maker, in this case was simply a 230v line fed from the power distribution panel and a control panel NMEA 2000 network connection.  We also had the power feed to the low pressure feed pump installed earlier.  All of these connections were fed to a power buss located in the upper section of the water maker.  I found that I had to lay the unit down on it's side to gain access to the power buss.  The photo below gives a close view of the electrical tray.

• While the water maker is on it's side with the cover removed, I wanted to show some detail of the automatic valving and plumbing that is under the covers of this unit.  To the right of the electrical tray we have automated valves, solenoids, flow sensors and plumbing that will allow this unit to make water and automatically fresh water flush as needed. 

•  With the water maker upright and once again mounted, the covers can be replaced and we can continue plumbing.  The items that will need to be plumbed in  are:
• Product water to the fresh water holding tank
• Salt water brine which will be discharged overboard
• Fresh water flush which in this case is an automatic operation of this model water maker
• Fresh water flush consists of valving off the salt water intake to the high pressure pump and opening up a fresh water valve.  This process then pumps fresh water through the pump, lines and most important the membrane.  The fresh water flush will be plumbed in from the pressurized water system and flow through a filter before being plumbed back into the pre-filters.  In this way, every part of the water maker system will be flushed with fresh water.  The water maker will signal a solenoid valve located on the top of the filter housing when the fresh water flush cycle begins.  Note the image below:

• The fresh water flush is very important because leaving salt water in the system will destroy the membrane and reduce the life of many other components of the water maker.   Sodium Metabisulphite can also be mixed into the fresh water when the system will not be used for extended periods.  This process is known as "Pickling".

This completes the installation of the Sea Recovery system and once it is tested and put into use, it should produce 700 gallons of tasty drinking water per day.

In the next post I will cover the choice of making your own water maker system and the regular maintenance that you should expect.  Thanks for your time and attention...best wishes from Watts Up Marine Services.

Refrigeration Upgrade - Digital Automation

More on the water maker installation coming soon, but today I wanted to spread the word about a product I have successfully installed numerous times in the past that will upgrade the older mechanical controls on marine refrigeration systems.  Full Gauge makes many different types of digital controls that are used in the commercial and industrial market. I have found that they also make some digital controls that work very nicely in a marine environment, as well.

Full Gauge MT 511Ril is a programmable digital thermostat that can control almost any refrigeration system up to 16 amps of power draw.  It can also be used with almost any air conditioning and heating systems with some minor modifications to the existing electrical.  It is a very cost effective way to improve temperature control and visibility.  I have found that this unit can be ordered and shipped for under $100 and can be installed with little effort.  It is easy on the eyes, can be installed anywhere on the boat with a footprint of 2.8" x 1" (71 mm x 28 mm) and a depth of 2.8" (71mm).  The MT 511Ril comes with the mounting clips to mount into a bulkhead or navigation station panel.


The major features of this control is that now the electronics can be installed anywhere and can be read easily without opening the refrigerator door.  It operates on 12-24v DC or 115v AC.  The digital sensor replaces the fragile capillary tube that older controls once used, therefore removing the distance constraint that the rotary controls once had.  It has the ability to control the temperature from  -58 to 211degrees F and also gives you an adjustable temperature differential between compressor-off to compressor-on.  This temperature differential can mean significant power savings when you are out to sea.

Another new model that I have just ordered for stock is the MT 511C, it has all of the same qualities and features yet is much easier to mount due to it's round hole pattern.  See the photo below.

Other temperature controllers made by Full Gauge also sense the build-up of frost on the evaporator.  These devices have two temperature sensors and compare the temperature differential between the evaporator plate and the freezer/refrigerator box.  When the temperature difference is too great, the unit will then shut off the compressor and wait for the temperature of the plate to get above freezing which will melt the ice.  Once it senses a "no ice" condition, the compressor continues to operate normally.

The MT 511 is a device I would recommend to anyone that has the older non-digital controls on their refrigerators, freezers, heaters and air conditioning units. Have you had any experience with this product?  Any stories to share regarding your older temperature controls?  Post them here!

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!