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The Hotline: Serious Education ... plus the most fun you can have in metal finishing. Ted Mooney, Webmaster

Corrosion caused by deionized water

Q. My company produces medical devices used for heating or cooling a patient. I keep getting warnings from internal sources to avoid using deionized water due to the corrosivity of deionized water, yet I can find no reference to corrosivity in any reference documents. Our units use stainless steel, copper and plastics for the wetted parts. Can someone shed any light on this?


Michael Boland
- Cincinnati, Ohio


A. I can only respond with limited knowledge. DI Water is "Hungry"; it is so clean that it is aggressive. In resin exchange, I have noted that since I am removing more cation (Ca, Mg, etc,) than anion that my final pH is <7. I think others can shed more light on this.

Jon Quirt
- Fridley, Minnesota


A. If you are recirculating the fluid, chances are the deionized water is dissolving enough of the copper and or stainless to make itself less corrosive to the stainless. However, if you are exchanging the water or you are seeing corrosion (look at the welds for the first sign of damage), adding a bit of sodium carbonate or another non-halogen soluble salt to the water should abate any corrosion in this situation. (you don't need very much to virtually eliminate the corrosive nature of water). If you require a food-grade additive for FDA approval, there are many to choose from. As stated before, avoid chlorides, fluorides, iodides & bromides, and try to keep the pH neutral or slightly basic.

Dale Woika
- Bellefonte, Pennsylvania


A. Michael,

It sure seems that Dale and Jon are right. D.I water is very aggressive and will leach out impurities with ease.

May I suggest you go to the local supplier/manufacturer of your D.I. water and find out what THEY USE ... and I think you might find it is PVC.

There are, of course, better plastics than PVC but why buy a Rolls when a Mini will do?

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Freeman Newton
White Rock, British Columbia, Canada

(It is our sad duty to advise that Freeman passed away April 21, 2012. R.I.P. old friend).


A. Typically distilled and/or deionized water can be effectively stored in tin-plated [substrate] (put any kind of steel or ceramic here). The old standby tin auto-oxidizes & forms a surface which has has a very low solubility index in water. As long as the pH is neutral, long term storage in tin is common. There are a lot of platers represented here on the website who can do tin plating.

Glass is also effective for storage of distilled and/or deionized water. The solubility of glass is extremely low and even ultrapure water will reach a saturation quickly at parts per billion--not really a scaling issue at all.

3XX Stainless is perfectly suited for storing distilled water--the only susceptible points in the stream might be the welds. Very smooth, clean and very passivated welds should be fine. Electropolished contact surfaces are even better. Storing very pure waters in PVC has limitations, even PVC listed as DWC or NSF-DW. There is still a problem with leaching, especially over time, notably on heating.

Dale Woika
- Bellefonte, Pennsylvania


Q. I have a somewhat similar question concerning the storage of deionized water. We have a 304SS deionized water storage tank with a 304SS cooling coil inside the tank. During production down times, we notice that the conductivity of the water is slowly creeping up. The calcium-chloride brine that we use to chill the water could definitely cause the conductivity to increase, but could it also be from corrosion at the pipe welds?

Clyde Carlson
PTFE Manufacturer - Decatur, Alabama


A. Potassium permanganate stabilizes pH in Deionized water.......

David Hubble
- JAX, Florida


A. Clyde, the conductivity in your tank is increasing because of the absorption of CO2 from air. The CO2 converts to carbonic acid in the water which causes the conductivity to increase and pH to go down to around 5.5.

Dale Swope
purified water equipment and service - Newark, Ohio

August 13, 2008

A. Michael and All

The DI water will corrode the Copper and lower grades of Stainless and can even leach the Chlorides from PVC Plastics. If your application only requires a low conductivity you could use RO water or a 2-bed DI system which produces water in the range of 10 - 20 ppm. Dale is also correct in the CO2 absorption this can be stopped through the use of a Nitrogen Blanket type system

matt denny
- Columbus, Ohio

December 22, 2009

Q. What is a good resource for determining what concentrations of what ions will reduce/ effectively eliminate DI water leaching of PVC (and other polymers) plasticizers/impurities? My company is running a test using DI water with a rather expensive custom built piece of test equipment, and we don't really require Type 1 ASTM DI water, but tap water is too "dirty". Part of our test involves filtration of the flow stream to measure fiber erosion of samples of Nukon fiberglass, and before we add the Nukon we're finding some whitish/bluish residue on our in-line, 5 micron filter. We're keeping the equipment clean-room clean, but after a few days this residue appears and hinders the flow through the filter. We're currently in the process of analyzing/characterizing the residue, but we suspect it's based on leachates from the PVC. The equipment is made of acrylic, PVC, polyester, and an epoxy-coated pump.

Thanks for your help!

James Furman
- Reno, Nevada

September 21, 2012

Q. I am cooling high voltage electronics with pressurized deionized water coming from a A-514 steel tank. We know that the DI water will slowly dissolve the steel. If I look at handbooks for water/ steel corrosion and fatigue life it depends highly on the surface finish and depth of pitting. Does DI water corrode pit into steel in the same way as tap or salt water or does it dissolve the steel in a uniform manner?

John Miller
- San Diego, California, USA

April 9, 2016

Q. Hi I am building a work station/ cabinet with a countertop, where they are using DI water and I am looking for a material for the counter top that won't corrode.
Any suggestions?
Best regards

Dave Briganti
- Trumbull, Connecticut, USA

April 2016

A. Hi Dave. This NASA document indicated no dissolution of titanium, type 1100 aluminum, or type 304 stainless steel in DI water. =>
Unfortunately, it doesn't seem to indicate anything about the conductivity of the DI water used in the test, and I suspect (but don't know) that it makes a difference. The "DI water" available in supermarkets is probably no more corrosive than ordinary tap water, and I'm confident of the NASA results for such mundane water. 18 megohm ultra purity DI water for integrated circuit fabrication might well be "hungry" and aggressive as some people say, but I think as long as you stay away from copper countertops you'll be okay. There are countless references which claim that 3xx series stainless is fine.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey

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