Does reverse osmosis water corrode copper plumbing? The answer ..

ohmmm_gwAugust 3, 2011

The answer is YES.

I did a very unscientific study of this. I had installed a typical under the kitchen sink RO filter with a storage tank.

And one day I decided to test the water on a piece of copper.

So I took a small glass jar and put RO water in it. Then I took a brand new copper tubing hold down clamp and dropped it in the water. I covered the jar with plastic wrap to prevent evaporation and then waited.

Nothing much happened the first week or so. I changed out the water with fresh RO now and then. And after a month I began to notice the water had an orange tint to it. Hmmmm.

So I continued to change the water out once a week or so.

After about 3 months of sitting in RO water, the photo results are posted below.

Now, I realize, I did not use an actual piece of copper pipe. But I can make a pretty good guess, that if I did, the results would be similar.

You can see the particulate matter in the water. And you will also see that on the paper towel that I poured the water through. The corrosive effect was enough to reveal the base metal used on the copper clamp.

So anyone thinking about doing a whole house RO unit, better think twice if you have copper plumbing. Even if you have pex tubing or similar, the plumbing fixtures themselves usually have copper tubes on them.

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justalurker

Sure it does... water is the universal solvent. When stripped of pretty much everything except the H and the O by an RO, water will try to dissolve and hold in suspension everything it can come in contact with.

What you are describing is called leaching and is why PE tubing is recommended for POU RO units.

Whole house RO units are not cost effective and require careful and thorough planning for complications such as leaching..

    Bookmark   August 3, 2011 at 1:17PM
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davidro1

water is the universal solvent.

in the laundry forum I once posted that I used the universe's greatest solvent in my washing machine, at no extra cost. I often wash with cold water.

    Bookmark   August 3, 2011 at 3:50PM
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theplbginfo

Also whole house RO is extremely inefficient using between 3 and 5 gallons of water to produce 1 gallon of drinking water. If you're at all interested in water conservation RO is not the right choice.

Sean
theplumbinginfo.com

    Bookmark   August 3, 2011 at 5:02PM
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justalurker

That statement should be... If you're at all interested in water conservation whole house RO is not the right choice

    Bookmark   August 3, 2011 at 5:11PM
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asolo

RO is wasteful. Softeners are wasteful. Just about everything "civilized" society does is "wasteful". Then, again, every conservation-minded person I know lives in the biggest house they can afford. And, where I live, they all have RO units under their sinks.

    Bookmark   August 3, 2011 at 5:33PM
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aliceinwonderland_id

Interesting, Sean, that your handle references plumbing and then you display a lack of basic plumbing knowledge. There are two things that can be done with an RO to nearly eliminate "waste" water (a complete misnomer if you understand water balance at all, but that is another discussion entirely).

1) Install a permeate pump, which will decrease "waste" flow per gallon of RO water produced.

2) Plumb RO "waste" water to the household water heater rather than to drain.

Quick, easy, inexpensive, and you can use your plumbing skills to accomplish the tasks.

    Bookmark   August 3, 2011 at 6:03PM
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asolo

Kinetico has at least two system designs that operate without back-pressure allowing much more efficient production. Assume others do, too, but don't know.

How does one plumb RO waste-water so it goes to the water heater....that is non-pressurized gravity-drained source....into pressurized source?

    Bookmark   August 3, 2011 at 7:05PM
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rjh2o

Just a thought to share. We can waste food, paper, gas, time, electricity and many other things. Almost all pollutants can be removed from water. So if every drop of water on the earth has been here for time eternal. How can we possibly waste any water?
RJ

    Bookmark   August 3, 2011 at 8:31PM
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asolo

Oh, wow.

    Bookmark   August 3, 2011 at 8:41PM
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justalurker

The law of conservation of water...

Water can neither be created nor destroyed... only billed for.

    Bookmark   August 3, 2011 at 9:02PM
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aliceinwonderland_id

asolo - The effluent from an RO is not at zero pressure. It is lower than inlet pressure, however. A pump and a couple of check valves and you're good to go. There are systems already designed to operate this way.

    Bookmark   August 3, 2011 at 10:02PM
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asolo

News to me. Thanks.

However, I can tell you the effluent from my RO systems -- now and for past 19 years -- has been and is, indeed, at zero pressure. The drain line goes directly into the zero-pressure drain-line under the sink.

If you say this can be handled, I have no argument......except for the zero-pressure one.

    Bookmark   August 3, 2011 at 10:16PM
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justalurker

Asolo,

"The effluent from an RO is not at zero pressure. It is lower than inlet pressure"

Alice is correct and if you think about it you will realize that the effluent on the drain side of the membrane is being pushed through the drain line by a portion of the line pressure that makes it through the membrane.

The simplest example of what Alice offered is... Watts Zero Waste RO

http://www.costco.com/Browse/Product.aspx?Prodid=10034720

And now there's a retrofit kit for existing RO installations.

https://www.wattspremier.com/products.php?product=Zero-Waste-Retrofit-Kit

You don't have to hook it up as the instructions illustrate. You can plumb it as Alice said if you know the correct way to do it.

    Bookmark   August 3, 2011 at 10:47PM
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asolo

The effluent from MY RO system -- past and present -- certainly IS at zero pressure. It exits down my sink's gravity drain. Where does yours go? If you're splitting hairs by saying there is enough "pressure" to get it to the entry-point of the sink's gravity-drain from the membrane cartridge, well, OK, ......but hardly the point I was making. I was comparing "practically zero" pressure effluent line against full-pressure hot-water line which I didn't understand.

Now I do....thanks.

    Bookmark   August 3, 2011 at 11:48PM
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justalurker

Asolo,

Let me see if I can explain this better.

Most ROs installed in the last 5 years or so have a code required air gap faucet.

Those faucets are higher (sink rim height) than the RO mounted under the sink.

If the effluent from an RO is under ZERO pressure (as your ROs are?) then how does the effluent get to the height of the air gap faucet so it can cross the air gap and get down to the drain?

Is it magic or is it pressure?

Alice said "Plumb RO "waste" water to the household water heater rather than to drain". To the WATER HEATER. He didn't say anything about the hot water line. One could plumb the effluent to the cold side of the water heater using appropriate flow control and the effluent is no longer wasted..

    Bookmark   August 4, 2011 at 12:33AM
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davidro1

atmospheric pressure.
This is "low".
This is an air gap.
Once water is ejected from any device, it is at that pressure.

Some devices can handle ejecting water out, into atmospheric pressure.

Whether or not a device will work well when it is expected to eject water out, into a pressurized line; This Is My Question.

-

I'm sure everyone can figure out that something additional can be rigged up, to take atmospheric pressure water and / pressurize it / pump it into a pressurized line.

I believe the deeper stronger question is whether or not there is an RO system or an add-on which puts the potentially wasted water back into the pressurized system, and which does so adroitly professionally and warranteedly.

" .... could plumb the effluent to the cold side of the water heater using appropriate flow control ..." Duh. I could have written that myself, and I have no idea what solutions there are!

"...and the effluent is no longer wasted" Ditto.

Hth

    Bookmark   August 4, 2011 at 10:30AM
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justalurker

Not atmospheric pressure... the pressure is that portion of the line pressure that pushed the water through the membrane.

"I believe the deeper stronger question is whether or not there is an RO system or an add-on which puts the potentially wasted water back into the pressurized system, and which does so adroitly professionally and warranteedly"

See my post above for links... Wed, Aug 3, 11 at 22:47

".... could plumb the effluent to the cold side of the water heater using appropriate flow control ..." Duh. I could have written that myself, and I have no idea what solutions there are"

Then the solution exceeds you plumbing knowledge. And to repeat what Alice said... "A pump and a couple of check valves and you're good to go. There are systems already designed to operate this way".

    Bookmark   August 4, 2011 at 10:49AM
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bus_driver

Test the strap with a magnet to see if it is steel that is just copper plated. One of the photos looked like plating that had flaked away. I know little about RO, and cannot make an informed comment about it.

    Bookmark   August 4, 2011 at 12:51PM
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aliceinwonderland_id

Most, if not all, copper straps are copper-plated steel. Corrosion of a copper strap will look different from corrosion of a copper pipe.

Copper is more susceptible to general etch corrosion (corrodes evenly over the entire surface). However, as plating on cheap parts tends to be uneven, corrosion is not visible until the thinnest spot is gone. At that point, copper in the water will deposit in discreet location on the carbon steel below, setting up galvanic corrosion - that is when you start seeing the rust in the water. Further corrosion of the carbon steel causes copper plating to flake from the surface.

A copper pipe corroding in RO water would appear different. The corrosion would be much less obvious because it would be so even. It would take long enough that if you were using purely visual cues to determine corrosion, you might come to the erroneous conclusion that corrosion was not taking place.

1 Like    Bookmark   August 5, 2011 at 12:20AM
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oriddlero

Found good info and thought i would paste here. The i have a continues TDS on my RO input and output and my output is currently around 40 PPM. The Output feeds my Ice-maker and my Instant hot through copper pipes.... I was worried about corrosion and possible leaks and the below paste makes me feel better!


Question:

Will putting a whole-house reverse osmosis (RO) system on a house with copper pipe cause leaks?

aquacareservice@embarqmail.com

Answer:

Will putting a whole-house reverse osmosis (RO) system on a house with copper pipe cause leaks?

aquacareservice@embarqmail.com

The simple answer to your question is yes. Copper plumbing that is exposed to RO water will cause pitting; however, the question begs for a more thorough explanation of whole-house RO. To begin with, when most people hear the term RO, they think of water that has had the mineral salts reduced by 99 percent. While this is good for life support water, this is not practical for domestic,whole-house, working water. It is good to keep in mind that the water for this type of application should have a finish TDS of 50-100 ppm.

The product water off the membrane should pass through a small column of calcite or equivalent product, or it can be treated with soda ash to neutralize the acidic nature of the water to a less corrosive state. Bear in mind that these products must meet the NSF standard for food service.

In addition to neutralizing the acid, calcite will add calcium carbonate to the water. If the water being treated by the RO still contains hardness, then an acid feed is generally needed to drop the pH to increase the solubility of the hardness. This will allow the membrane to reject high levels of hardness while preventing scaling. Therefore, passing the water through a softener to remove any remaining hardness is a very efficient way to provide the kind of working water that most homeowners would like in the first place.

Gary Battenberg, Technical Director, Hague Quality Water International

As a rule of thumb, if the TDS (total dissolved solids) concentration of the RO water is above 10 ppm (almost all is >10), it should not be aggressive enough to dissolve copper and cause leaks.

    Bookmark   last Friday at 9:25AM
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aliceinwonderland_id

This should NOT make you feel better about running RO water through copper TUBING.

  1. The above quotes (and if you cut and paste you really ought to provide a link or a citation) are addressing the use of whole house RO water through copper PIPES, which are either schedule 40 or schedule 80. Copper tubing, on the other hand is very, very thin and much more susceptible to pinhole leaks.
  2. You haven't provided your water's pH - the lower it is, the more corrosion you will have.
  3. The "rule of thumb" portion indicating that 10 ppm is not aggressive enough to dissolve copper is just plain incorrect as written. I suspect the gentleman was either hurried or his comment was edited. If he meant that it wouldn't be likely to cause leaks in pipes where water is pH-buffered, possibly correct, but tubing, as stated previously, is an entirely different matter. Further, if pH is below 7, copper pipe for RO water is a bad idea. RO water is nearly always below a pH of 7. 40 ppm RO water is aggressive enough to dissolve copper.
  4. Your RO water is your drinking water. The EPA action level for copper in drinking water is only 1.3 ppm - that's quite low. You could easily have that much copper in the you water after running through copper tubing, particularly if it has been sitting stagnant for an hour or more between uses.

Using copper tubing to distribute RO water is just asking for trouble.

    Bookmark   last Friday at 10:16AM
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oriddlero

Here is a link to address your citation scolding: http://www.wcponline.com/expertview.cfm?ID=3717 

I have not measured the PH of the RO output recently, but when i last measured it it was right around 7.

I can fairly easily replace the copper with Poly all the way up the input for the refrigerator and input for the instant-hot fairly easily, however the instant-hot output has a ~12" copper tubing lead soldered to it (to handle very hot temperatures) so i guess i am beat there. Thoughts?

#4 is an excellent point. I was actually thinking about that but i was not aware of the EPA action level and how to measure it. This alone is reason for concern. Thanks.

    Bookmark   last Friday at 11:26AM
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aliceinwonderland_id

There are very few drinking-water heaters that are rated for RO water. The ones that are rated for RO water use stainless steel tanks and tubing. The ones that aren't use carbon steel tanks and copper tubing.

    Bookmark   last Friday at 11:34AM
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oriddlero

Ugh. So one day my $400 instant-hot is going to explode in a steaming hot fireball of lava likely to destroy everything within a 10' radius?!

Okay, maybe not, but you are making me think I should just pull the RO line off the instant-hot and feed it tap water from under the sink (ugh). Even if i were to hack the instant hot with a hot-water rated poly-line, the internal tank would still be susceptible to corrosion and the RO water may strip it and contaminate my drinking water. Maybe ill put a cheapo standard filter under the sink just for the instant hot.

I'll replace the copper line to the refrigerator with RO rated poly to be safe. Thanks for the SOLID info! Its hard to find real data from educated people on this subject.

BTW.. Congratulations, I am your first follower.

    Bookmark   last Friday at 12:00PM
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aliceinwonderland_id

Ignorance is bliss, right up to the point where it isn't, right?

If it were my house, I would either plumb tap water to the existing instant-hot or replace it with one that is RO rated. Quick&Hot used to make one, but I haven't looked at them in about seven years so that may no longer be the case.

    Bookmark   22 hours ago
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