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Old 04-05-2009, 20:11   #1
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Do Watermakers Work in Fresh Water?

OK that might be a totally dumb question, but the manufacturer sites don't actually mention whether watermakers also provide potable water from fresh water or brackish water. Does anyone know?
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Old 04-05-2009, 20:20   #2
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Yes they'll work. You'll get better output from them than you would in seawater too.
The way they work is essentially like a really fine filter.
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Old 04-05-2009, 20:27   #3
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I have a GE unit under my sink at home. I wonder if they could be adapted to marine use? Would sure be cheaper.
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Old 04-05-2009, 21:06   #4
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Quote:
I have a GE unit under my sink at home. I wonder if they could be adapted to marine use? Would sure be cheaper.
Sort of depends on what GE unit it is. With salt water, aqueous salts are filtered at the molecular level. That pretty much is as as good as any filter gets. We have a GE filter on the fridge ice maker at the house. It works good for that. I wouldn't use one on the boat for anything but maybe a pre filter on a water maker.
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Old 04-05-2009, 21:22   #5
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I have a GE unit under my sink at home. I wonder if they could be adapted to marine use? Would sure be cheaper.
Covered in another thread. Pressure required is dependant on salt concentration. All you have to do is change everything designed to work at around 100 psi on your under sink RO to work at 1000 psi.

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Old 04-05-2009, 21:22   #6
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The GE unit I have is a RO unit, not just a filter.
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Old 04-05-2009, 22:57   #7
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Originally Posted by drew.ward View Post
OK that might be a totally dumb question, but the manufacturer sites don't actually mention whether watermakers also provide potable water from fresh water or brackish water. Does anyone know?
Going back to the original question: Yes, it should work just fine, though I wouldn't trust it to remove biological contaminants. You will need to dial down the pressure though! For example, on my Village Marine, instead of the 800PSI for salt water, it's around 200PSI for fresh water. Basically what you want to do is keep the ratio of product vs discharge within spec.

Don't forget to take care of your prefilters, they won't last nearly as long in dirty water!
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Old 04-05-2009, 22:59   #8
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Yeah that was one issue I was predicting...somehow I had this image of green slime filling the very expensive RO unit.
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Old 05-05-2009, 04:42   #9
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The GE unit I have is a RO unit, not just a filter.

Still won't work. Under the sink type RO systems and salt water RO systems are totally different animals. Though I suppose you could fit a GE RO unit on a boat if you were using it in fresh water, but you wouldn't be happy with the results. The energy required to make the small amount of water provided doesn't make sense.
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Old 05-05-2009, 08:52   #10
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Folks, please look at the original post, this topic is about using a watermaker in fresh water, NOT adapting an under-sink GE RO filter. sparty should have started a new topic for that discussion...
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Old 05-05-2009, 09:03   #11
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Most RO units are designed for use in "Clean open ocean waters" according to the manufacturers. The primary issue is not the salt content of the water, but the particulate content. Most fresh/brackish areas have so much biological and non-biological particulate matter that the prefilters would rapidly clog and you would be unable to maintain an adequate supply of water to the unit. This may not be true of some fresh water areas now that zebra mussels have clarified those waters but it is generally true.
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Old 05-05-2009, 09:36   #12
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Capt'n Bill - Out of desperation I ran my RO watermaker here in Falmouth Harbour, Antigua yesterday. The filters clogged within an hour

To the original topic - My manual has curves for salt content and temperature and pressures that wouldn't go off the chart in fresh water and I see no reason that they won't work in fresh water.
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Old 05-05-2009, 10:20   #13
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So I wonder if the trick would be to run the fresh water through a primary filter first where you could get rid of the bio matter with a filter that's not quite as fine as the normal pre-filters (and not as expensive). Then allow that water into the system.
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Old 05-05-2009, 10:49   #14
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Katadyn sells a silt reduction kit for use in brackish water and inland waterways. It adds a pressure boost pump and a finer secondary filter element.
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Old 05-05-2009, 11:46   #15
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It's true basic marine based watermakers work best in the open clean ocean. But RO is RO. There are land based units that work in brackish, salt, fresh, rivers, streams, dirty wells, etc. and are placed in some pretty exotic places such as Africa. The primary difference between the two is in the pre-filtering. If for some reason you needed to often run your marine based unit in fresh, brackish or silty water you would need to upgrade your pre-filtration. Wouldn't be the first time it's been done, but it usually doesn't make sense for freshwater pleasure boats to have watermakers in the first place.
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