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"Deionized water vs. Distilled water in heat exchanger"


Q. We have a YAG laser welder for welding stainless steel hermetic load cells at our facility, we use deionized instead of distilled water in the heat exchanger. There are some people that say that it may be messing up the lamps. I say that DI water is better (We've been using it for over 3 years). Can you tell me why DI water has an expiration date and why it is hazardous if you drink it?

Todd Weaver
- Hopkinton, Massachusetts


A. I don't know why DI has an expiration date, but you don't want to drink it. Osmotic pressure across the stomach cell walls when filled with DI water will cause bleeding.

James Totter
James Totter, CEF
- Tallahassee, Florida


A. Deionized water is exactly that -- water that has essentially been stripped of all of its ions. Water likes to be balanced in its natural state, however, and this means that it adds ions to itself to achieve that goal. Therefore, DI water grabs ions from everything it touches that can be dissolved or absorbed. It is about a close as you can get to a Universal Solvent. In your case, it will extract metals from all of the brass fittings you have, and will also pull carbon dioxide from the air - you get the drift.

Osmotic Shock

Its hazardous to you to ingest because of what is called osmotic shock. Your body on a cellular level is balanced to a degree by the amount of salt that your cells have in them. This salt allows electrical signals to travel through your nervous system, creates reactions in your muscles that make them move, and also keep most simple bacteria from killing you because they cannot live in a high salinity environment.

Back to osmotic shock - your cellular walls allow the free passage of water and salt through them. A process called osmosis means that the concentration of salts try to achieve equilibrium by moving to establish similar concentrations through your whole body. If you drink DI water, however, the absence of salt in it makes this movement occur VERY fast, as the body starts to try to reach equilibrium. Unfortunately, the salt movement is so fast and has so much force behind it that the cell walls basically explode from the shock, which of course kills the cells. Kill too many and you can get internal bleeding and all kinds of nasty stuff like that.

Distilled water is not nearly as aggressive as deionized, and it is essentially balanced. It still has very little ions in it, but it is less aggressive than DI and while I would not recommend drinking it either, is less likely to harm you. It also is not corrosive to most metallic internal parts on your welder.

tom baker
Tom Baker
wastewater treatment specialist - Warminster, Pennsylvania


thumbs up signOH NO (screams of pain and anguish). My wife gave me a glass of totally pure water and my stomach is going to bleed and my cells explode ... if only she had given me the polluted stuff I would be OK. Hang on a second I am just checking to see if these posts were on April 1st.

I have wiped the tears from my eyes and the hysterical laughter has subsided so let me continue.

The responses predicting dire consequences are absolutely correct. Osmotic shock is a real phenomenon and it will lyse cells (yup they will explode. OK OK they gently break apart without any earth shattering detonation). What you were not told is that tap water will do EXACTLY the same thing. On the face of it one could conclude that drinking beer is safer than drinking water but my wife still won't buy that one. Now for the rest of the story. The difference between the osmotic pressure of blood and tap water, de-ionized water and distilled water are almost identical. All three will lyse cells to the same degree. If you want to drink tap water, de-ionized water or distilled water then go ahead. The thing you should not do is inject any of them into your bloodstream. That would be bad. In hospital, when they give you fluid intravenously, they give you normal saline. That is salty water that has had its osmotic pressure adjusted to match blood. While normal saline is safe and will not cause your blood to explode or your stomach to bleed it makes a terrible cup of tea. By the way, I have been working with blood, blood products and designing hemodialysis, plasmaphoresis and tissue culture machines for 26 years and have drunk hundreds of gallons of de-ionized water in that time.

De-ionized (DI) water is water in which the ions have been removed. (Ions are simply dissolved chemicals that have an electrical charge) You can remove the ions in a number of ways. You can do it by using anion and cation exchange resins in a variety of configurations. In the best cases this will give you 17 megohm water which is very pure. Distillation will do the exact same thing. And the third commonly used technique is dual reverse osmosis (RO) which can also give you ultra pure water. The little machines you see at the supermarket where you can fill up a jug with pure water use single reverse osmosis and what you are buying is city water that has been de-ionized (well, sort of de-ionized, they remove 95% of the ions).

There is not a lot of difference between them except that anion and cation exchange resins may not remove any colloidal silica that may have been in the feed water. Under some conditions you can get a build up of silica which is almost impossible to remove. At the other end of the scale, distilled water does not have any colloidal silica and is bacteriologically pure as well (which is not necessarily true with RO water or DI water). Frankly, it does not matter, at all, which of the three you choose -- your laser will work fine.

As for the expiration date which seems silly but isn't. DI water is very low in ions and as Tom Baker pointed out it is hungry for ions. In time it will leach ions from the container so it is less de-ionized as time goes on. In reagent grade chemistry it may interfere with the result of a subtle and sensitive experiment; but in your case, no problem.

Hope your YAG keeps cranking out the coherent photons for years to come.

John Holroyd
- Elkhorn, Wisconsin


A. Distilled water is the least expensive and most readily available coolant for this application.

The primer: most potable tap water has minerals and gasses dissolved within, from metal carbonates and halogens, to traces of other compounds and a few organic contaminants. Carbonates have a fairly narrow range of solubility in water with respect to temperature, and as you cool the water close to and below freezing or heat the water over 100 degrees, the dissolved carbonates tend to precipitate out of solution as scale. Scale buildup in plumbing or cooling systems is undesirable because it reduces water flow in the system and also insulates the heat-exchange capabilities of a cooling/heating system. Most other contaminants are not particularly troublesome in cooling systems, as scaling does not generally occur. It just happens that carbonate scale is not readily soluble in water.

Water can be treated to reduce the carbonates in water to prevent scaling.

One method is to employ very strong magnets on the feed water. This is a controversial treatment, which is said to modify the carbonate component to somehow deposit as aragonite as opposed to the calcite structure of typical scale; the theory is based on the fact aragonite has a somewhat more soluble range in water than calcite, hence, there should be less scaling. As a materials scientist I am fundamentally skeptical of this process but in all honesty I did place some of these on a large evaporative cooling process; although there was a normal amount of precipitated minerals in the system, the minerals did not seem to scale on the ID of the system. Go figure.

Softening the water is a process of ion-exchange, where the calcium and magnesium components of the scale minerals are replaced by sodium or potassium. The net effect is markedly reduced scaling in a system because sodium and potassium carbonates are very soluble in water over a wide range of temperatures and pH; these chemicals do not come out of solution and if they did, they would redissolve. Soluble chemicals=no scale. There is usually no problem with softened water in a closed cooling or heating system, but in an evaporative cooling situation there is still the issue of minerals being concentrated in the water from evaporative loss of the water. Softened water is usually completely a safe alternative for heat exchange, but with a 200,000 dollar laser system, I might be more apt to use the next method, distillation.

Distillation is used to remove all of the dissolved solids from a water. The water is made into a vapor using heat or reduced pressure (or both) over the feed water, and the vapor is condensed into a distilled water. Non volatile components of the water, i.e. scale minerals, are left behind. The end product will likely still have all of the volatile and most of the organic components of the feed water, and depending of the process, there may still be a few traces of dissolved solids. The total dissolved solids in distilled water are probably less than 50 parts per million and should be less than 10 ppm. The dissolved gasses and trace contaminants will likely have a small ionic component and the dissolved gasses will probably affect the pH of the water slightly. Whereas softened water will not corrode most metals, there is a possibility distilled water will corrode metals and frequently does. Distilled water is a notorious solvent for stainless steel welds. In a close! d cooling or heat exchange system, a few minerals are frequently added to reduce the potential for corrosion, and sodium carbonate (washing soda) [affil. link to info/product on Amazon] is a candidate. Distilled water is as inexpensive as bottled water and is just as available. If you need more than a few gallons, call your local water bottler & arrange for a tanker truck to make a delivery. If it was ~my~ laser system, I would use distilled water with a bit of electrolyte for corrosion inhibition.

Deionized water is usually distilled water that is run over a bed of styrene plastic beads with various ion-exchange materials bonded to them. The ions in the water are adsorbed and bonded to the surface of the ion-exchange resin in the beds of beads; the resulting post-treatment water will have most of if not practically all of the ionic load removed. The net effect is very pure water. One caveat here is the dissolved solids which are not ionic will likely remain in the solution, as well as dissolved organics. Also, the ion-exchange beds are relatively expensive and have a finite capacity for ionic exchange which decreases arithmetically during use. DI water tends to be aggressive toward some metals, but the price of DI water usually places it out of the range of machine cooling. There are some procedures which DI is perfectly suited for, but not for making process water.

In the chemistry and analysis industry, distilled+ deionized water is often treated with carbon and other adsorbent materials to make ultrapure water with is then vacuum degassed. Ultrapure water must be stored in nickel or tin oxide, sealed tightly against the atmosphere. It is very difficult to work with. Medical water is often distilled and deionized water with is then ozonated to remove pyrogens.

"Water Quality & Treatment"
by American Water Works Association
from Abe Books

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Another method of removing scale potential is reverse osmosis. Reverse osmosis is effectively using a very small-pored filter for the water; the pores in the membranes are tiny can actually filter out molecules. However, to effectively remove ionic components the water must be pretreated to flocculate scaling materials before treatment. R.O. is probably best used as a drinking water ultrafiltration process, in combination with other treatments.

As for the relative potability of the pure waters, the difference in waters is very small. There is no adverse health affect from drinking distilled or deionized water. Deionized water tastes kind of bland & somewhat insipid, and distilled water has no taste at all. Some people get used to these qualities & drink them all the time. In either case, the taste is improved by aeration--if you shake the pure waters up with some air, the taste improves. The taste of any given water is largely imparted by the various mineral components; many of the drinking waters on the market today are, in fact, purified tap water to which minerals have been added (Avalon, etc). By law, drinking waters can not have more than 1000 parts per million of dissolved solids, so when you get down to the analysis of most available waters, there really isn't much difference between tap water, mineral water, or purified waters (no nutritional difference at all between any of them!)

As far as the health issue is concerned, it is true, water is hypotonic to cells & will destroy them. However, tap water is also hypotonic to cells. Your skin & stomach & intestinal linings are perfectly suited for thriving in and processing water. If you were to inject water into your blood, cells would die. If you cut your skin & wash the wound, the exposed cells do die. Fortunately, the fats that lyse out of the exposed wound quickly makes the wound less susceptible to water damage. Any ultrapure water you drink will quickly dissolve some saliva from your mouth--as soon as it has dissolved few parts per million of any substance, it is no longer ultrapure anyway. If it is a concern & all you have to drink is ultrapure water, you can stir the water with a metal stainless spoon or your finger first & it will magically transform itself from ultrapure water to just water.

So, in conclusion, to cool the laser, filtered and softened water would probably work, but I would used treated/ distilled for an expensive toy like a laser.

Dale Woika
- Bellefonte, Pennsylvania

November 25, 2010

A. For large scale uses, de-ionized (DI) water is usually cheaper than distilled water. Most large ships now make DI water rather than by distillation. In the old days when steam engines were the means of propulsion, distilled water was essentially a by-product.

As for drinking DI or distilled water, neither are toxic when ingested in normal amounts (the same amounts as you would drink tap-water). DI and distilled water are both much purer than tap water, but they both taste very 'flat', lacking the trace amounts of impurities that are in regular city water.

As for 'osmotic shock', forget it! From the perspective of the cells in your body there is little difference between the osmotic pressure of tap water and DI or distilled water.

As for DI water having an expiry date, this is of importance when the use for which ultra-pure water is sensitive to small traces of contaminants. High purity water is an extremely good solvent and will fairly rapidly dissolve trace amounts of minerals/metals even from glass or plastic containers.

Mike Vince
Retired chemist/toxicologist - Delta, BC, Canada


thumbsdownA. I can say from experience that DI water is not a healthy drink. We had a customer that had to keep sending an employee home for health reasons. This person worked around our tool, so they were suspicious that our tool was causing the problem. They finally observed the employee taking drinks from the water gun that we provide with our tool and dispenses DI water. Once he stopped drinking from the DI gun, the problem went away.

Craig Meuchel
- Kalispell, Montana


A. I would imagine that some DI water is not contaminant free water as such would be very expensive and sold as such. The substrate used as well as any chelating/bonding chemicals could cause illnesses like cyanosis.

It is recommended when drinking large quantities of water that it contain some sodium. There are other positive ions in the body as well as negative ions. The recommendation is specific only to sodium however. The organs do not remove sodium well and it is equally taxing to replenish. The correct concentration entering is whatever would maintain stasis in regards to what leaves. Which is a good rule of thumb for all the ions, really.

I drink distilled water and I am not dead (yet).

J. M. McCandless
- Philadelphia, Pennsylvania

September 23, 2008

Q. How do you turn a brand new aluminum radiator into a sprinkler?
A: Fill it with DI water

This comes from a radiator engineer, not a chemist, so please forgive my layman approach.

DI water robs ions from the inside of the fluid flowing circuit (radiator, engine, laser, pump, etc). The radiator core tubes are typically the thinnest material in the circuit at approx. .013" thick, so it doesn't take long for the radiator to develop leaks. The use of ionically balanced clean water with corrosion protection additives (whatever the manufacturer recommends for coolant) is the best practice.

Jim Cusimano
- Mooresville, North Carolina

October 8, 2008

Q. What is the chemical difference between DI and DW? Will we use this DW in place of DI in LASER m/c coolant?

Abhishek Gupta
user - MUMBAI, India

August 26, 2009

Q. Air is dissolved in water to some extent, this is undesirable for my experiment. What should I use, deionized water or distilled water?

Bhawna Verma
student - Varanasi, U.P., India

November 13, 2009

A. Reply to "Air is dissolved in water to some extent...""

Doesn't matter. What you want instead is to put the sample under a slight vacuum to remove the trapped air. Had a process where just pumping it created trapped air. @ 3 neg. was enough, when it happens ... it's very sudden. It'll look like fizzy pop.

David Jaxs
- Dayton, Ohio

April 22, 2010

Q. I am researching the care of a bronze sculpture fountain. This discussion seemed very pertinent. Our primary concern (more so than cleaning) is preserving the golden patina of the bronze. It was sealed with an indoor/outdoor lacquer immediately after polishing. I am wondering about the wisdom of using a water softener in distilled water? Thanks for any advise.

John Hobson
- Walnut Creek, California

May 10, 2010

A. Hi, John. I can't see traditional softened water having any bad effect on your fountain. Softening simply substitutes sodium or potassium for the calcium in the water, and shouldn't make it more corrosive or aggressive.


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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