Do Watermakers Work in Fresh Water?

[Highlander40]

Open ocean water has plenty of bio load.
Maybe more than freshwater.

[TurtleTime]

My recently installed Village Marine 450 gpd specifically says no fresh or brackish water use.

[Farfanugon]

Originally Posted by drew.ward

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?

I know this is a OLD post , but i had the same question a few days ago , and it took me 3 days to find a defiant answer , the cut and dry is NO you should never use a desalination unit in fresh water to make drinking water , The Desalination Unit removes very little of the micro organisms and bacteria from the water, And as the world oceans become more and more polluted even ocean water harvested threw a Desalination Unit should be purified before drinking ,
A survival freshwater purification unit with filter "good for 500 Gal" will run you less than 50 bucks . And give you very safe drinking water , removing 99.9999% of all bacteria from any fresh water .
50 bucks for a 3 year supply of safe drinking water is not a bad trade off ,No matter how you do the math. just Ebay search " SURVIVAL FRESHWATER PURIFICATION " to get more info on these units , even a $10 survival straw will get you 50 Gals of safe drinking water.
There is no point getting Dysentery over $10-50 ...

[colemj]

No, that is not correct.

A reverse osmosis desalinator will remove close to 100% of bacteria, viruses and other micro-organisms.

An under-sink filtration unit will not. An under-skin RO unit will.

So if one adjusts the pressures and flows correctly, a RO unit can make good safe water in fresh water.

Mark

[J Clark H356]

I researched this issue a couple of years ago. You can use a watermaker in freshwater. Cruise RO said all you do is set the flow rate of the unit and the pressure varies for conditions of salinity. I was t,hinting about putting one onto cruise. I couldn't find a good space for what I wanted, so decided that I could get fresh water pretty frequently in marinas along my proposed route - but wasn't sure about how good the various water sources would be. I was very concerned about water quality, so I just installed a SafeH2O unit this weekend that will use my tank water and purify to a really high standard. In fact, I could use my wash down system to fill my water tank and drink the purified water. I don't plan on doing that, but it,is possible in freshwater rivers and lakes. With this high a standard, I now won't worry about what is in the base water I take on.

[Farfanugon]

Originally Posted by colemj

No, that is not correct.

A reverse osmosis desalinator will remove close to 100% of bacteria, viruses and other micro-organisms.

An under-sink filtration unit will not. An under-skin RO unit will.

So if one adjusts the pressures and flows correctly, a RO unit can make good safe water in fresh water.

Mark

This is 100% NOT what the people at PUR told me. they assured me my Survivor 35 Desalinator Manual Reverse Osmosis Water Purification unit is not intended for fresh water use and that the bacteria in fresh water are far different than bacteria found in salt water , And that PUR makes no claim that there Desalinator can or will remove a safe amount of fresh water bacteria.

Not wanting to sound like a wanker , But i trust PUR more than a random forums post, Everyone should where there safety , and the safety of there children is involved . Its took me 3 days to get a reply from PUR which is why i felt the need to share there reply here. some may be in a hurry and not have 3 days to await a reply .

[colemj]

Originally Posted by Farfanugon

This is 100% NOT what the people at PUR told me. they assured me my Survivor 35 Desalinator Manual Reverse Osmosis Water Purification unit is not intended for fresh water use and that the bacteria in fresh water are far different than bacteria found in salt water , And that PUR makes no claim that there Desalinator can or will remove a safe amount of fresh water bacteria.

Not wanting to sound like a wanker , But i trust PUR more than a random forums post, Everyone should where there safety , and the safety of there children is involved . Its took me 3 days to get a reply from PUR which is why i felt the need to share there reply here. some may be in a hurry and not have 3 days to await a reply .

I think you misunderstood PUR.

Just think about it logically, and let's reason through: yes, the TYPES of bacteria in fresh and salt water can be different, but the SIZE of bacteria do not vary much between the two.

RO membranes filter on size. The average pore size in a RO membrane is less than a nanometer. This allows it to filter out single molecules of salt and other things.

Bacteria are composed of millions or billions of single molecules. The typical sizes of bacteria are around a micrometer or so. The smallest bacterium known is 0.5 micrometers (yes, it is found in fresh water, but isn't harmful to humans). Viruses are generally smaller, but the smallest virus known is 5 nanometers.

So the pore size of RO membranes is over a thousand times smaller than the size of a bacteria and 5-1000 times smaller than viruses.

To put this in perspective, it would be similar to you trying to pass yourself through a 1/16" hole (which is ~1000 times smaller than the average human).

There is no way a bacteria is going to make it through RO membrane pores.

I suspect that PUR told you that its Survivor 35 could not be run in fresh water because they cannot control the pressure sufficiently to prevent membrane damage. If pressure is not controlled, fissures can develop in the membrane that can pass bacteria. This would not be noticeable in fresh water like it would in salt water. Fresh water can harbor human-harmful bacteria and you could be infected. You may have heard, or conflated, separate pieces of advice from them into meaning that RO systems cannot be run in fresh water because of bacteria.

If they indeed told you that fresh water bacteria and viruses could pass through an RO membrane while salt water ones were fine, they were wrong. You can take that to the bank.

RO systems can be operated with no problems in fresh water as long as pressures and flows can be properly adjusted.

And even on forums, you will find people with advanced degrees and long careers in specific areas that know far more than the people working in company tech support.

Mark

[Tellie]

Gotta go with colemj on this Farfanugon. I can't really add much at all but here is a simple chart to give you an idea of the filtration of a salt water RO system that might help visually. Hope it comes through.


The Osmonics Filtration Spectrum

[colemj]

And note that the particle size scale on that chart is logarithmic, not linear.

Mark

[Captain Bill]

Originally Posted by Farfanugon

This is 100% NOT what the people at PUR told me. they assured me my Survivor 35 Desalinator Manual Reverse Osmosis Water Purification unit is not intended for fresh water use and that the bacteria in fresh water are far different than bacteria found in salt water , And that PUR makes no claim that there Desalinator can or will remove a safe amount of fresh water bacteria.

Not wanting to sound like a wanker , But i trust PUR more than a random forums post, Everyone should where there safety , and the safety of there children is involved . Its took me 3 days to get a reply from PUR which is why i felt the need to share there reply here. some may be in a hurry and not have 3 days to await a reply .

I don't know exactly what was said to you, but I suspect that what they meant was don't use thier RO units in fresh water. Katadyn (formerly PUR) RO units run at fixed pressures and flows. You cannot adjust them for proper functioning in fresh water. I used to be a marine biologist and took graduate courses in both marine and freshwater microbiology. Nothing living in either environment is getting through an intact RO membrane. One concern they might have is what if the membrane is not intact. In salt water you would get high salinity water and it would not pass the TDS test so you would know you had a problem. If you have a hole in a membrane used in fresh water there might be little apparent change in the TDS reading, so how would you know the water was safe to drink? By the way I own a PUR RO unit.

[AnchorageGuy]

We used our Village Marine watermaker on fresh water lakes for years with no problems and no ill affects. I can't see where fresh water would be any more contaminated than salt water under the right conditions. There were many instances where we would not use our watermaker in salt water because of pollution and contaminates. Chuck

[svmariane]

All very well, but there is another solution. We use a "Water Fixer 1000" when taking on dock water in "iffy" locations. I see no reason it couldn't function afloat, as it would only take the addition of a pump (with strainer) to draw water aboard.

Heck, we even use it to process rain water to counter atmospheric pollution.

{edit: Could even hook it into the water-maker system if doubts exist about ocean pollution.}

Unit has two filters: (5.0 micron and 0.5 micron) with an UV light to kill the nasty thingies.

Check it out: Ultraviolet Water Filters And Purifiers Model 1000

Works for us.

James

[Sea Frog]

Originally Posted by Farfanugon

This is 100% NOT what the people at PUR told me. they assured me my Survivor 35 Desalinator Manual Reverse Osmosis Water Purification unit is not intended for fresh water use and that the bacteria in fresh water are far different than bacteria found in salt water , And that PUR makes no claim that there Desalinator can or will remove a safe amount of fresh water bacteria.

Of course they make no claim. This is a normal practice in a society where people sue each other for whatever stupid reason they may come up with. So every manufacturer tries to limit responsibiliy as much as possible, PUR too. Their disclaimers, however, do not have anything to do with a real world and whether their equipment will be working in fresh water environment, they just gave you their lawer's talk. OF COURSE as any RO system they WILL work and absolutely yes they will remove bacteria and such, as folks above stated, but if you try doing that, and something goes wrong, you will lose your warranty, that's what PUR is telling you.

[Farfanugon]

Originally Posted by Sea Frog

Of course they make no claim. This is a normal practice in a society where people sue each other for whatever stupid reason they may come up with. So every manufacturer tries to limit responsibiliy as much as possible, PUR too. Their disclaimers, however, do not have anything to do with a real world and whether their equipment will be working in fresh water environment, they just gave you their lawer's talk. OF COURSE as any RO system they WILL work and absolutely yes they will remove bacteria and such, as folks above stated, but if you try doing that, and something goes wrong, you will lose your warranty, that's what PUR is telling you.

OK this has the most logic in it to me, I still think ill use the $50 fresh water unit, its 500 gal and filters are 4 for 50 bucks. Ill be in need of a fresh water unit for less than 3 weeks

[ghaffy]

My 2 ct:

I built my RO watermaker myself, during the winter 2009/2010, based on one Filmtec SW30-2540 membrane and (at the beginning) an ordinary pressure washer for 59.99 as the high pressure pump. The unit is in use since then, still flawlessly working. Details here: Dido's Watermaker


The summers we spend on the Mediterranean. There it works as an "ordinary watermaker", i.e. producing fresh water from sea water.

The rest of the year our boat is berthed at the River Danube (Vienna, Austria, Europe).

Sometimes we use the watermaker to make drinking water also on the (fresh water) Danube.

I'd almost like to say: of course, this works.

But you have to take 2 things into consideration:

#1: You need a RO-unit that you may regulate manually. The osmotic pressure of saltwater is somewhat around 430 psi. This means you have to apply signifcantly more pressure than 430 psi to start fresh water flowing from the membrane (this is why common systems are run at some 800 psi).

When you use a saltwater membrane with fresh water as feedwater, then you'll realize that the permeate starts to flow already at some 50 psi. If you increase the pressure permeate flow will also increase, more or less linearly. Thus, running your watermaker with fresh water as feedwater at the "usual" pressure of 800 psi will certainly damage the system.
When we use it on the Danube (very, vary rarely) we apply some 70 to 100 psi, which results in flow rates of some 30 gph permeate.
This, btw, needs only ridiculous little energy (compared to salt water operation).

#2: Danube water (and most water of rivers) does not at all meet the clarity of open sea water in terms of sediments etc. Thus (here at the Danube), the pre-filters are really quickly clogged (at the Mediterranean the first of our 4 pre-filters may be used for 4 weeks or so without need of cleaning/replacement. On the Danube it is rather a question of hours, although the water of the Danube - in terms of contamination, bio-hazards, toxins etc. in our area is "class 1b" to "class 2", where "class 1" and "class 1a" is drinking water quality). It is "micro-sand" and harmless other particulate matter, like some sorts of algae etc. that rapidly clogg the pre-filters.

(But the clogging-issue might be none on bigger and "clear" lakes).

So my answer to the initial question, whether watermakers work with fresh water, too, is simply: YES, they do. I know this by experience.

BR
Andreas
Vienna, Austria, Europe