Where to find the cheapest RO de-salination membranes

[gathem]

Originally Posted by pparra

Gathem,

How much water do you intend to produce per hour? I assume that you already made a research to find good prices for pressure pump. Which one are you going to use? How much for that?

Tks in advance for the info and good luck with your project!

I was planning to do something similar to the Dido DIY watermaker.
My proposed bill of materials:
Booster pump:$60 - 120VAC 50PSI self priming pump
Motor / pump: $110 120VAC pressure washer
Pre-filters: $75 Fully Assembled Module #3A:
Pressure vessel: $450 Module #2C Water Maker Pressure Vessel
RO Membrane: $187 2.5" x 40" Dow Filmtec SW30-2540 RO Membrane

I will also get a high pressure gauge, pressure regulator, pressure release valve, so I can adjust the pressure going to the membrane. My family owns a shop which supplies hoses/motors/gauges/fittings etc so I plan to just go there, and pick and choose parts and assemble it there. I have no idea on the costs of these items.

With only one membrane, and using only about 60% of the pressure the membrane is capable of handling, I expect 6-8 GPH (based on Dido's reports). If I needed more I could add a second membrane/housing in series, and would expect 10-14 GPH.

Grand total: $882 (plus whatever the hoses/gauges/fittings/regulators cost, and the cost of learning...)

My needs are very simple, I just want to plug it in, and fill my tanks. Flush it with fresh water, and store the unit below. If the pump goes, its only $100, and small enough I could keep a spare. I only plan to use it weekly at most.

[Cheechako]

Yep, been there done that twice. You specified most of what you need. you need a good needle valve for pressure control, a pressure gauge and probably a 3 way to choose overboard or in the tank. Make sure the motor /pump you buy will handle the pressure your membrane needs ....
Not sure of life of a pressure pump that's not designed for salt water... the bores may pit while it sits unused...

[captlloyd]

Originally Posted by gathem

Id like to ask everyone to stop questioning my ability to build the damn thing and focus on the actual question. I just stated that I was building a simple water maker.

I've read most of the articles/posts about DIY water makers. Theres a difference between a go-cart and a commuter car. If I needed to get to work every day I wouldn't buy a go-cart. In this case, I just want a stand alone unit, which I can plug into and outlet, swing a couple hoses over the side, and produce some drinking water. I don't want to tie in to the boats electrical/tank/through hulls. I know all about the pressure vessels, pickling, running fresh water through it after, maintenance, etc.

I don't want to delay cruising by saving up for an additional $4000 for a water maker.





I'm not "reinventing the wheel", i'm simply reducing complexity.
I just want a diy version of this without spending $5000:


Thanks to those who provided links to low cost membranes

Don't know a thing about water-makers but please ignore all the negative post. We all don't have deep pockets and I applaud someone willing to put some thought and elbow-grease into something they can't afford to buy outright. I see the same negativity when people want to restore boats all the time. Good luck and let us know how it turns out, good or bad. I would not think anything less of you even if it doesn't work out.

[gathem]

I'm not sure of the life of the pressure washer pump either, but @ $110 I could buy a new one every season, and keep a spare on board and save a bunch. There is a good deal of information about the cheap pressure washers lifespans in Dido's thread. I think the general experience is "They last a while".

I don't require reliability as much as I require cheap, and easy to fix.

[MonaOnR3]

Originally Posted by gathem

I require cheap, and easy to fix.

For some strange reason I dont believe those two go hand in hand..
But what do I know.. I'm just a cruiser..

[Captain Bill]

Originally Posted by gathem

I was planning to do something similar to the Dido DIY watermaker.
My proposed bill of materials:
Booster pump:$60 - 120VAC 50PSI self priming pump
Motor / pump: $110 120VAC pressure washer
Pre-filters: $75 Fully Assembled Module #3A:
Pressure vessel: $450 Module #2C Water Maker Pressure Vessel
RO Membrane: $187 2.5" x 40" Dow Filmtec SW30-2540 RO Membrane

I will also get a high pressure gauge, pressure regulator, pressure release valve, so I can adjust the pressure going to the membrane. My family owns a shop which supplies hoses/motors/gauges/fittings etc so I plan to just go there, and pick and choose parts and assemble it there. I have no idea on the costs of these items.

With only one membrane, and using only about 60% of the pressure the membrane is capable of handling, I expect 6-8 GPH (based on Dido's reports). If I needed more I could add a second membrane/housing in series, and would expect 10-14 GPH.

Grand total: $882 (plus whatever the hoses/gauges/fittings/regulators cost, and the cost of learning...)

My needs are very simple, I just want to plug it in, and fill my tanks. Flush it with fresh water, and store the unit below. If the pump goes, its only $100, and small enough I could keep a spare. I only plan to use it weekly at most.

For your target output and your hp pump capacity you do not need a 40" membrane. A 2.5x 21 inch is plenty. It will put out up to 12.5 gph if you have enough flow and pressure. You can get 15-20% of your HP pump's output through the membrane. The issue is that 20% requires 1000 psi which will reduce the life of the membrane over running it at the normal 800 psi. Odds are you might as well run it at the high pressure because the rust from your cheap high pressure pump will ruin the membrane faster than normal anyway. I went with a cheap pump and the membrane lasted about 4 months before I started having water quality issues. I religiously flushed it with fresh water after each use and despite this the thing was heavily contaminated with rust. Even though I had a pump with "stainless check valves and ceramic pistons it still rusted severely in a just a couple of uses. My brine discharge line was translucent PEX and it was severely stained with rust by the second use. High pressure seawater is way harder on metal than low pressure. I seriously doubt that the pump you are proposing to use will hold up as well as the nearly $400 pump (motor not included) that I was using. I suggest that you buy several of them if you are going to be out any length of time. You might want to keep a spare membrane handy if you are going to be out 6 months or more. You need 800 psi, 60% of 1000 PSI isn't going to cut it. You really don't get any significant output at 600 PSI, at 700 you get a little, but it does not really start flowing until you get to around 800. My guess is that your boost pump is not made of a marine grade alloy and wont last very long at all. All "Aluminum" is not created equal. You can certainly make a watermaker that will work a few times with the items you propose, but I would not count on it lasting too long. I wasted a lot of money doing it on the cheap. Nice thing was the intake filters, TDS meter, and membrane holder were able to be salvaged so I won't need to buy them again when I do it right.

[Steadman Uhlich]

Originally Posted by Captain Bill

For your target output and your hp pump capacity you do not need a 40" membrane. A 2.5x 21 inch is plenty. It will put out up to 12.5 gph if you have enough flow and pressure. You can get 15-20% of your HP pump's output through the membrane. The issue is that 20% requires 1000 psi which will reduce the life of the membrane over running it at the normal 800 psi. Odds are you might as well run it at the high pressure because the rust from your cheap high pressure pump will ruin the membrane faster than normal anyway. I went with a cheap pump and the membrane lasted about 4 months before I started having water quality issues. I religiously flushed it with fresh water after each use and despite this the thing was heavily contaminated with rust. Even though I had a pump with "stainless check valves and ceramic pistons it still rusted severely in a just a couple of uses. My brine discharge line was translucent PEX and it was severely stained with rust by the second use. High pressure seawater is way harder on metal than low pressure. I seriously doubt that the pump you are proposing to use will hold up as well as the nearly $400 pump (motor not included) that I was using. I suggest that you buy several of them if you are going to be out any length of time. You might want to keep a spare membrane handy if you are going to be out 6 months or more. You need 800 psi, 60% of 1000 PSI isn't going to cut it. You really don't get any significant output at 600 PSI, at 700 you get a little, but it does not really start flowing until you get to around 800. My guess is that your boost pump is not made of a marine grade alloy and wont last very long at all. All "Aluminum" is not created equal. You can certainly make a watermaker that will work a few times with the items you propose, but I would not count on it lasting too long. I wasted a lot of money doing it on the cheap. Nice thing was the intake filters, TDS meter, and membrane holder were able to be salvaged so I won't need to buy them again when I do it right.

Thanks for posting your comments above.

I think you made several good points. I found your description good and helpful.

I especially like that you pointed out that initial functioning to "specs" may not be a good indicator of an effective solution, since materials may deteriorate faster than expected due to the marine environment (salt water).

As I see it, what may work once or a few times during development or in testing (or in the workshop or at the dock before a voyage), may also quickly fail in real world use or in a shorter time than expected (e.g. when cruising or on a passage and when it is really needed). That is one reason I don't find the "cheap untested/unproven" equipment to be the best or most reliable solution, especially if one's life may depend on it.

[Tellie]

The thing with DIY watermakers is, as was pointed out above, is the attempts to reinvent the wheel on a one off built system. You are simply just not going to run two 40" membranes from an electrical pressure pump salvaged from a Home Depot pressure cleaner, I don't care how cheap you find membranes. They had better be cheap because you are going to go through a lot of them. There are two factors in a properly working watermaker, pressure is just half the equation, flow is the second. Generating 3000psi in a $150 Home Depot pressure washer is simple, just neck down the opening. The problem is flow. There's a reason professional painters and pressure cleaning companies spend several thousand dollars on a commercial grade fuel driven 3000psi pressure cleaners. As you pointed out above "I don't require reliability as much as I require cheap, and easy to fix". Well you had better like fixing and discounting reliability if you are going to go this cheap. I assure you, you will be fixing a lot and cheap and reliability will be holding hands as they fly right out your port window, probably with a good portion of your wallet. I say the following with confidence, as I've probably built more DIY watermakers starting years ago than anyone on CF knows. Even building a DIY watermaker with the right parts is going to get closer to the 3-4K range for most first time DIYers and that also means the hundreds of hours spent pursuing this is time that you get to volunteer for free, time better spent on other projects or cruising. As also stated above, you don't have to listen to the naysayers, but you might want to learn from the ObiWans in the watermaker business as we have been down this road many, many, times before. The least expensive way you are going to get a decent watermaker is as suggested above, talk to Rich Boren. You may think even his systems are too expensive for your taste. But I assure you, you will need advice, one more time, you will need advice, the extra cost of one of his systems is going to be worth every penny after the first phone call to him. The sailing environment is an extremly tough environment. It plays havoc on even the best of marine equipment. Can you build this Rube Goldberg watermaker? Sure you can, there are even Youtube videos on how to build Home Depot weed eater outboards. But I wouldn't want one of those powering my boat either. Look, I don't mean to sound like a smart ass. But I've seen this before and it just never ends well. Buy the right thing the first time and you won't have to buy it again. Good Luck.

www.HaldenMarineService.com

[hellosailor]

If it could be made "cheap and easy" and good enough to work weekly but last a full year, I think we'd see that pump being sold by Harbor Freight.(G)


But forgetting that, all of this is relatively old technology. The pumps, the membranes, the whole concept and list of supplies has been relatively unchanged for 20? years. Now ask yourself, "Why hasn't anyone come back on the internet and posted a blog or reply that says they built one of these even TEN years ago, and it has kept on working well enough all this time?"


I think the answer is that a dirt cheap RO system just won't cut it. Maybe it will work as well as a "Power Survivor" or other hand-operated system in limited use. Maybe...


But then I'm a pessimist, I'd be DELIGHTED if Ganthem comes back to us, once a year over the next decade, and says "Nyah nyah! My desalinator is STILL WORKING y'all. Still giving me 1 hundred gallons every week, five thousand a year, after xx years!"


I honestly would. More power to you, Ganthem.

[Stu Jackson]

Tellie noted it quite well, as did hellosailor.

If it had been done before...

That's why I first said don't reinvent the wheel.

Now you have a bunch of reasons for why I said that.

Good luck anyway.

[matureee]

Don't listen to the naysayers and go for it. Though the points about rust are valid.

You don't need an excessive flow rate. You need enough to replace the water going through the membrane plus enough to prevent the concentration of salt in the HP water from rising too much.

I run a system which I have home built around a Spectra Clarke HP pump I believe that it is better than the original in that the LP water flow path is "straight line" with the number of bends and connections reduced as much as possible to reduce losses.

Good luck with the project.

[hellosailor]

Stu, you forgot one.


Carbonated beverage sales have been down for years. I remember when Evian and mineral water were rip-offs targeted to Yuppies and everyone said that would never add up to anything. Today? You can't find water fountain, even in public buildings, and bottled water is BIG BUSINESS.


So, come on now, how about at least considering that expensive water-makers are a result of Coke and Pepsi trying to price people out of the DIY-bottled-water market?


(VBG)

[Captain Bill]

Originally Posted by matureee

Don't listen to the naysayers and go for it. Though the points about rust are valid.

You don't need an excessive flow rate. You need enough to replace the water going through the membrane plus enough to prevent the concentration of salt in the HP water from rising too much.

I run a system which I have home built around a Spectra Clarke HP pump I believe that it is better than the original in that the LP water flow path is "straight line" with the number of bends and connections reduced as much as possible to reduce losses.

Good luck with the project.

Odd that you would suggest he go forward with crap pumping hardware when you chose instead to do it with an actual water maker pump. No one said you can't build your own water maker, but using components that were never designed to be in contact with high pressure salt water it is simply not going to last. I have no doubt one can build a more efficient water maker than some commercial units. Some of their decisions are based on marketing where you can make decisions based on function if you choose to do so such as more direct line flow routing because you are not trying to make it fit in the smallest possible box.

[nimblemotors]

Dido's WM did work, you did read his blog, right? Did it last 10 years? No. And if you read the blog, you should come to the conclusion the cheap electric pressure washers are not the way to go, so if the OP's plan is to use them, I agree this is not a good plan.

Now if you take one and modify it to be more durable and salt-water friendly, it might work OK. But first see how loud they are, you need to modify that part too!

[Canibul]

I'm in the same general boat, in that I need a decent watermaker between now and November and don't yet have the $ 4000 for a 20 gph one. I was wondering what happens when people upgrade from a watermaker the size of the one we need ( 20-30 gph ac powered would be great) to one that lets them run a condomaran with four staterooms, four heads with showers, and a washing machine.

Is there much of a market for used watermaker supplies from those who have upgraded to larger systems? I'm okay with a box of components. This is not rocket surgery.