DIY Watermaker: Pros & Cons

[Therapy]

Nice compilation S/V Pizzazz.

[Celestialsailor]

Originally Posted by Pizzazz

Dears,

Following recent discussions I updated my watermaker design spreadsheet (attached). A couple of notes for everyone attempting a DIY watermaker. First, it is hard to beat the watermaker package from Cruise RO/Rich Boren. He uses top quality parts, pump, motor and everything comes ready to assemble. Based on my analysis his package is nearly 3x less expensive than the large commercial offerings per gph fresh water produced.

Thus, if you want a 20 gph AC watermaker, you go to Rich. It produces water at the equivalent of DC 5 amps/gallon. Now, if you want something smaller which would mean DC powered then it gets interesting. There are three options:

1. Spectra at around 1.2 amps per gallon, approx. $1000 investment per gph capacity. Very efficient but in my opinion unreasonably expensive.

2. The Katadyn units (best to find a used Powersurvivor 35 or build your own drive for the surplus units on ebay.com). The investment is $300 per gph, makes water at 4 amps/gallon. Great units but you have to leave them on nearly continuously to make useable amounts of water (possible as they make little noise especially insulated).

3. Build your own with a DC motor and pump from ebay. Various combinations work, the best seems to be 1/3 hp motor with 0.5 gph pump driving a 2.5x21" membrane giving you around 6 gallons per hour and you can go up from here. You can expect around 4 amps per gallon if you run your membrane at high flow with 20% recovery or down to 2.5 amps per gallon if you starve the membrane for water and force it to run up to 35% recovery. The cost in terms of investment per gph will be similar to Rich's with substandard components (brass pump instead of stainless, etc.) and the initial investment will be lower but in the long run it is probably not worth it.

The key benefit and the reason for this post is this starvation mode, where you feed the membrane with very little water (e.g. 0.5 gpm flow for a 40" membrane) which allows high recovery and low amps per gallon. 2.5 amps/gallon can be achieved at one quarter of the cost of a Spectra unit. This is at the cost of possible shorter membrane life (non-issue due to negligible cost) and possibly higher salinity (i.e. instead of getting 200 ppm and below you might be getting 500 ppm and below). What do you think about the higher salinity? We put salt in the meals anyway so may be it is not that bad.

Feel free to add your experiences to the worksheet, it would be good to keep a record of our experiences.

S/V Pizzazz

I think you forgot to add into Cruise RO the cost of the Honda 2000 and the gas cost per gallon.

[jcapo]

Originally Posted by TickMan

Ok, so this is not a problem ? Can you tell me estimate, how many GPH are you making ?

13gph at 12.2 vols at the motor in fairly high salinity water. 15gph with 13.5 volts at the motor in the same water. That's at 800psi.

[TickMan]

Originally Posted by jcapo

13gph at 12.2 vols at the motor in fairly high salinity water. 15gph with 13.5 volts at the motor in the same water. That's at 800psi.

Thank you, this is very good result, I will try to build my own, based on your recomendation.

[TickMan]

Hello guys

I bought this motor but haven't success with Pump ( pump from Ebay wasn't new, so in procees of return )

Found this pump but MAX RPM for pump 1750 but motor is 1800 RPM, so pump will operate with higher RPM. Should I worry about it ? Or with DC power from battery RPM still will be lower ? Any siggestion ? Or I need to find another pump ? If yes, this is only two type of RPM 1750 or 3400 RPM. What is better ? If pump rotating slow than normal ? or opposite ?
Thank in advance

[ghaffy]

Hello TickMan,
there is no reason to worry about RPM:
a) You'll probably need a device to increase RPM slowly from zero to full speed. If so then you may run the pump at any RPM between lowest (see manual, something about 700 RPM) and max (1750).
b) the 1800 RPM rating of the motor is a theoretical number. DC motors run faster at 14.7 Volts (when the engine is running and the alternator delivers current) and more slowly at 11.8 Volts (no engine running). Anyway, the difference of nominal 50 RPM do not count in reality.
Neither will you run the pump at 1750 RPM nor will the motor run at 1800 RPM in real life.

BUT:
The motor from your Amazon link is a 0.5 HP motor.
Now, there is a simple formula for every high pressure piston pump to find out what HP you need.
The formula goes like this

Required Power [kW] = (0.26 * gpm * psi)/475

When we use the specs of your pump:
(0.26 * 2 gpm * 800 psi)/475 = 0.88 kW

0.88 kW equals ~1.2 HP

If you try to run the pump with a 1/2 HP motor neither will it deliver 2 gpm nor will it reach anything close to 800 psi.

Sorry to say.
I built my WM on my own from scratch. This little motor won't work in a "1st generation water maker" (i.e. plunger pump plus SW30 Filmtec membrane).

[a64pilot]

The other thing to add into your build your own costing is how much of the wrong stuff will you buy and how much driving around will you do or how much shipping will cost.
There are a lot of hidden costs. I believe your not going to save any money and a direct drive D.C. Watermaker is going to kill your battery bank. I'd go AC and a generator as most have to have a generator to get by without a watermaker, unlikely you have the excess power to run one.
However what you will get is the satisfaction of having designed and built it yourself, and sometimes that is very worthwhile

[Jsta_Rebel]

Originally Posted by a64pilot

The other thing to add into your build your own costing is how much of the wrong stuff will you buy and how much driving around will you do or how much shipping will cost.
There are a lot of hidden costs. I believe your not going to save any money and a direct drive D.C. Watermaker is going to kill your battery bank. I'd go AC and a generator as most have to have a generator to get by without a watermaker, unlikely you have the excess power to run one.
However what you will get is the satisfaction of having designed and built it yourself, and sometimes that is very worthwhile

You're right about a DC watermaker killing your battery bank, and I've also seen membrane flow rates on this thread that caused a giggle too.. Putting together a SWRO system isn't rocket science. There are some rules that need to be followed for flow and flux rates but the rest is just simple plumbing. What I can't figure out is why people wanting to build their own RO are trying to make it DC powered and are just not using AC or running their HP pump off of the motor. It's much easier and most cruisers run their engines from time to time anyway. You can really make a lot of water quick running the pump off of the boats main engine.

[SV THIRD DAY]

Originally Posted by Jsta_Rebel

What I can't figure out is why people wanting to build their own RO are trying to make it DC powered and are just not using AC or running their HP pump off of the motor. It's much easier and most cruisers run their engines from time to time anyway. You can really make a lot of water quick running the pump off of the boats main engine.

Because they don't know what they don't know yet.

Thinking you can run a 40A DC load off of a battery bank (non LiFePO4) using wind, solar and batteries is a classic mistake that then limits the water maker run time to when either a generator or alternator us running.

I help DIY water maker guys all the time and the sooner they get some professional help the less money they will waste on ebay mismatched pumps and motor sizes. I see the mistakes all the time.

Download our SM20 Simple manual as a good starting point and copy away...don't waste your time and money reinventing the wheel.

www.cruiserowaterandpower.com/uploads/smsimple.pdf

[Jsta_Rebel]

I don't have to reinvent the wheel. Installing a cat pump with a 12v clutch running off the engine has been done for years. The beauty of it is that you can step up to 4" membranes and make 40 GPH or even more without having to worry about how you're going to drive an electric motor. The solenoids or MBV's , conductivity monitors, and even pressure transmitters if you wish to use them are all low voltage, so setting up a pre-flush as well as a permeate post flush, and having a digital control panel is fairly easy to come up with. Swedgelock fittings including the needle valve for controlling the concentrate discharge and HP tubing is readily available as are the filter housings. The membrane flows are readily available online at Filmtec as are the curves for the cat pump. Last, yeah, I know the cat pumps are old technology compared to the Danfoss, but they are more user friendly and I've yet to see an end user pull down his Danfoss to replace the valve assembly or swashplate. How many of the Danfoss owners even understand what happens to this pump if it is starved for water for even just a few seconds?? Ohhh so that's what these bleed screws on the side of the pump is for they would say..

I'm all for keeping things simple on a boat. You can't go wrong. Many boat owners buy their watermaker, and you guys make a good one by the way, but many just can't afford them, and there are other alternatives available for making water aboard, but I've always found keeping it simple is always best.

[TickMan]

Originally Posted by Jsta_Rebel

I don't have to reinvent the wheel. Installing a cat pump with a 12v clutch running off the engine has been done for years.

Do you have GenSet ? I still don't understand what type WaterMaker do I need. I know not 12 VDC, Ok, will return this motor. But If I have GenSet, why I need Engine driven ? I can start GenSet or use Marine power to produce water. I want to go Caribian for 3 monts and will have only one month to prepare my boat for cruise. I have 360 Amps House batteries I want Install Solar Panels ( over davits ) not sure how many will fit, think 360 W, but main question for me is water maker.
1- Membrane SW30-2540 ( Do I need one ot two ? ) What some watermaker has one or two ? Do you will get more water ? ( or can use it just longer without replacement )
2- If I need 800PSI. why Pump must be 2000PSI or even more ? Or 800 PSI is minumum ? What is the maximum ?

I have very small cruise expirince and every day we have used main engine, to setup main sail and drop ancor and etc. I will think 1 hour per day or more, but do you have any days, when you don't need the main engine ? I assume yes, so why use main engine if you have GenSet for example ? Just curious

[TickMan]

Originally Posted by SV THIRD DAY

http://www.cruiserowaterandpower.com...s/smsimple.pdf

Very great manual, will take a look, thank you so much

[Celestialsailor]

Originally Posted by Jsta_Rebel

I'm all for keeping things simple on a boat. You can't go wrong.

Hmm...I think I have heard this a few times

[SV THIRD DAY]

Originally Posted by TickMan

But If I have GenSet, why I need Engine driven ? I can start GenSet or use Marine power to produce water.

You don't!
Installing an engine driven water maker when you have a diesel genset that you will be running 2-3 times a week for battery charging or hot water making would be insanity in my book as someone who builds and more importantly services water makers 7 days a week. The most trouble free water maker out there is a AC unit using a rock solid and dependable piston pump coupled to a 1.0 or 1.5Hp motor running off a genset and feeing 1 or two 40" membranes. It just doesn't get any simpler than that.

Engine driven water maker are in my opinion the worst way to go...why...
Because I have a little more troubleshooting history and the average bear, so I know how difficult it is to actually get the engine mount fabricated correctly, then manage to get the 4.2GPM of needed boost pump flow TO the inlet of the engine driven pump....not as easy as it sounds for the DIY guy and I help them fix this costly mistake all the time. Remember I HAD an engine driven water maker on my boat as we cruised Mexico and what do I have now? What did I change it to as Fast as I could? Yep...an AC powered unit from my generator. Why? Maintenance and reliability baby, there is nothing easier.

To your question about 1 or 2 pressure vessels and membranes>
Well that's just determined by how much water you want to make (and making sure your Hp Pump can supply the minimum flow for either 1 or 2 membranes)...so it's totally up to you, your Budget, Your mounting space, etc.

A 1.6GPM Hp pump will make 20GPH and use 9A from a 1.0Hp motor that can be powered by a Honda 2000 or diesel genset from a single 40" membrane (1100W). Now add a second 40" membrane in series to the first and you will make 33GPH for the EXACT same power usage. See the advantage of that now? Either 50% less generator time to make the same amount of water OR use 50% more water for FREE. The Dual membrane is also better because of redundancy. If one of your Two RO Membranes was to fail on you, no problem, just run your water maker on a single 40" membrane until you get a $197 replacement that is available around the world or sent to you DHL for $100 to $150 anywhere in the world in 3-7 days.

There is also a reason why water maker companies for small boats and Yachts are not using the 4" in diameter membranes and it isn't a Conspiracy by Big Water or Big RO to screw you. It's because the 4" RO Membranes have a 4GPM brine exit flow Minimum requirement to keep them healthy and from plugging up and becoming trash early. 4GPM on the brine exit my friends is HUGE and just isn't something you can reasonably do on a small cruising boat due to power requirements. But Rich...but Rich...I know a Guy...ya ya ya.... Well I know and worked with the Founder of Osmonics who invented and R&D-ed the current Polyamide RO Membranes and have worked with him in the R&D Lab doing the testing...so I'll take my real life quantitative data experience over a "but I know a guy". And you guys thought I was just a smart ass cruising Bozo...

I always joke with clients that I will only sell them an Engine Driven water maker after I first try to talk them out of it...I call it the Siren Song of water makers. I sold 5 engine driven water makers in 2016 and I sold 213 AC electric driven water makers in 2016. The vast majority of the AC units were also dual membrane water makers. Now who where the clients that needed the most Customer Service and Help...yep...the 5 Engine driven guys!

[Jsta_Rebel]

Originally Posted by TickMan

Do you have GenSet ? I still don't understand what type WaterMaker do I need. I know not 12 VDC, Ok, will return this motor. But If I have GenSet, why I need Engine driven ? I can start GenSet or use Marine power to produce water. I want to go Caribian for 3 monts and will have only one month to prepare my boat for cruise. I have 360 Amps House batteries I want Install Solar Panels ( over davits ) not sure how many will fit, think 360 W, but main question for me is water maker.
1- Membrane SW30-2540 ( Do I need one ot two ? ) What some watermaker has one or two ? Do you will get more water ? ( or can use it just longer without replacement )
2- If I need 800PSI. why Pump must be 2000PSI or even more ? Or 800 PSI is minumum ? What is the maximum ?

I have very small cruise expirince and every day we have used main engine, to setup main sail and drop ancor and etc. I will think 1 hour per day or more, but do you have any days, when you don't need the main engine ? I assume yes, so why use main engine if you have GenSet for example ? Just curious

No I don't have a gen set. I'm all 12volt. There are several different watermakers on the market, and you need to decide which one suits you best. I also have a lot of room in my engine room so mounting the pump to utilize the engine for power was not too difficult. A 2540 membrane will produce around 20gph. Two will produce twice that amount, but will require additional feed water flow. Yes a cat pump or PD Plunger pump will product extreme pressures but if you look at the pump curve, you will notice that it makes a heck of a lot more water at 800psi then it does at the higher pressures. The proper size pump is everything when sizing an RO. Here is a link for information on sizing. http://www.catpumps.com/products/pdfs/993330A_CAT_Sys_Design_Guide.pdf

Most cruisers do use their engines with some using them more than others which is why for some boaters, an engine driven RO system makes sense. Not saying it's right for everyone, but it suits many boaties just fine. The same way as many have engine driven refrigeration systems with cold plates. One other advantage the engine RO systems have is the ability to run a larger pump just as effectively as a smaller one without having to make electricity for it. I have two 4"x 40"SW30-4040's on my boat that make around 80 gallons per hour total. However, I do commercial / Industrial desalination systems for a living in the Caribbean so the 4" membranes fit my needs well but only because I have an engine driven pump that can produce sufficient feed water flow to them.

If a person can afford to buy a pre made system, it's probably the best idea and Rich makes a decent watermaker. I'm not too keen on the spectra units. To those that can't afford a watermaker or are looking to make RO water aboard on the cheap, there are alternatives to buying one off of the shelf. As I've said before, it's not rocket science, it's just water treatment and parts are readily available.