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post #1 of 10 Old 04-27-2019 Thread Starter
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The cheapest RO membrane on market

Hi. I am looking for the cheapest reverse membrane for sea water (and housing). I have been searching up and down on ebay and google, but I don't feel more competent, so figured asking here for info. The cheapest I have found so far is a 4" 40" membrane w/housing for $500 included shipping.

The membrane can be smaller, as long as I can support my daily water consumption.


Thanks in advance!
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post #2 of 10 Old 04-27-2019
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Re: The cheapest RO membrane on market

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Originally Posted by Halvard View Post
Hi. I am looking for the cheapest reverse membrane for sea water (and housing). I have been searching up and down on ebay and google, but I don't feel more competent, so figured asking here for info. The cheapest I have found so far is a 4" 40" membrane w/housing for $500 included shipping.

The membrane can be smaller, as long as I can support my daily water consumption.


Thanks in advance!
I don't think you will do much better on a good 42" housing that has the capacity to take 1000 to 1200psi. When you think of that much pressure, do you even want to think about a cheap housing?

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

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post #3 of 10 Old 04-27-2019 Thread Starter
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Re: The cheapest RO membrane on market

Good point, it can't compromise on strength. I was thinking about a smaller housing and membrane only. The 4" 40" is capable of producing way more water than I need.

EDIT:
I have come across Dow Filmtec SW30-2521, which is 2.5" x 21". But the only hosuing I have found that fits supports 300 psi (stainless steel)......

Last edited by Halvard; 04-27-2019 at 01:41 PM.
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Re: The cheapest RO membrane on market

It sounds like you are approaching building a watermaker from the wrong end. You don't say exactly what you are doing, but nobody searches for random dimensions in membranes for their watermakers.

If you get a standard size membrane - 2521, 2540, 2580 - these all have numerous sources for pressure vessels suitable for seawater RO. I don't have any experience with the 4" sizes.

I just bought 2 Dow Filmtech SW30-2540 membranes from AmericanRO.com for $175 each. This is the lowest price for those membranes I know of. They also sell housing for all of the common sizes: SEAWATER HOUSINGS PRESSURE VESSELS

Again, you asked about 2.5"x21" membranes, as well as 4"x40" membranes. This suggests that you might not understand watermakers, or what you really need. One cannot just connect any random size membrane to any random volume pump and have a watermaker that works. A larger membrane does not produce more water than a smaller one if you cannot pump enough water at pressure through it.

I guarantee that if you found a 4" membrane of any length with a suitable pressure vessel for $500 that is is not for seawater RO. You need to understand this difference if you are building a watermaker.

If you describe better all of the watermaker components you already have, it would be easier to provide help.

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Re: The cheapest RO membrane on market

I am trying to find the smallest and cheapest membrane w/housing (same dimensions of course). I was thinking of using a high pressure washer as my pump - with does things in place I basically have a water maker.... but will add sediment filters pre membrane (20 and 5 micron), psi gauge and one-way vales.

As stated in my last post, the smallest sea water membrane I have found is 2.5" x 21".. But the 2.5" x 21" housing I found only handled 300 psi. I thought the latter might be meant for brakish water. Maybe I have misunderstood how pressure works.

Thanks for your reply and link coleMJ.. Will definitely look into the company!

EDIT:
The company you suggested was exactly what I was looking for!! They have 2.5" x 21" membrane and high pressure vessel in the same size. Now, I just need to cross my fingers they ship internationally for a good price.

Last edited by Halvard; 04-27-2019 at 07:41 PM.
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Re: The cheapest RO membrane on market

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I was thinking of using a high pressure washer as my pump
Sorry, but again, don't you think if high-pressure washer pumps would work adequately for an RO system, all of us who built our own and all the companies making RO units would use them @$300.00 instead of $2k to 2500?
I'm sorry, but I suggest you'd best do a lot more reading up on watermakers. There is a multitude of good info on the web.
When I built this 35 to 40 gph unit, the first thing I bought was the pump. It took me four months of searching the web, but I got a great $2200.00 pump for $940.00. Then, I purchased the other parts to match the pump. That was the cheap and easy part.
It has been working fine for 7 years, with one membrane change a couple of years ago.

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post #7 of 10 Old 04-27-2019
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Re: The cheapest RO membrane on market

There is no way a pressure washer pump will drive a 4" membrane, so you can forget about those. In addition to the membrane, pressure vessel, and pressure washer pump, you will need high pressure hoses and appropriate fittings, a good quality needle valve, a pressure gauge, a prefilter housing and filter, and an assortment of valves, tubing, and fittings. Almost all of the cost will be in the pump, membrane, pressure vessel, and needle valve.

I don't know what you think you will pay in the end for all of the above, but it likely won't be much less than just ordering one of these: https://seawaterpro.com/shop?olsPage...watermaker-kit

The type of system you are pursuing runs off AC power, so I assume you have the electricity to run this - either a generator, or a large battery bank and inverter. Also, anecdotal reports from people using pressure washer pumps for watermakers show them needing replacement pumps every year or so. The pumps are cheap - $100 - but if you plan on using this watermaker for several years, the cost does add up eventually.

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Re: The cheapest RO membrane on market

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Sorry, but again, don't you think if high-pressure washer pumps would work adequately for an RO system, all of us who built our own and all the companies making RO units would use them @$300.00 instead of $2k to 2500?
Actually, there are several companies selling inexpensive watermakers using cheap pressure washer pumps. And countless DIY people building them. There are tradeoffs - pump lifespan isn't great, but the pumps only cost $80-100. The rest of the system is like any other watermaker.

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Re: The cheapest RO membrane on market

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Actually, there are several companies selling inexpensive watermakers using cheap pressure washer pumps. And countless DIY people building them. There are tradeoffs - pump lifespan isn't great, but the pumps only cost $80-100. The rest of the system is like any other watermaker.

Mark
Every part of my watermaker and any I'd ever use would be 100% food service grade. Ceramic pump valves and seats, not just cheap steel. But I'm kinda that way when it comes to putting air or nourishment into my body.

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Re: The cheapest RO membrane on market

I think you misunderstand how a watermaker and reverse osmosis works. Nothing on the pump side is getting through the RO membrane. Nothing on even the best pumps is food service grade. You can push raw sewage through the cheapest pumps and an RO membrane and get safe water out of it.

It might make you feel better to think you have food service grade components, and that they are providing you higher quality water, but the facts are neither of those are true.

FWIW, the Karcher pumps used in most of these cheap systems are not cheap steel. They aren't even metal of any type.

The only downsides to the cheap systems are breakdowns and lifespan. Water quality and safety is the same when they are working.

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