The "Hungry Water" Theory


Is distilled water better for your car's radiator than plain old tap water? That was the question Tom and Ray fielded this week from John in Columbus, Ohio, as he was trying to prolong the life of the new radiator in his diesel GMC van. (You can hear the call right here.)

Ray advanced a certain dubious-sounding "hungry water" theory he heard about from a chemist, in which distilled water actually pulls out more minerals than regular old water, increasing the likelihood of radiator problems.

Ray sounded convinced... but what do you think? Is there such a thing as "hungry water" -- and will it cause unanticipated hassles for your engine's cooling system? Share your thoughts here!


I’m not a chemist, but there are rules where I work that say not to clean electronic parts like circuit boards with distilled water, or maybe the rule is to not use de-ionized water. I’m be very interested for someone with real knowledge of this to reply.

But of course I went to Wikipedia, and they have a page on distilled water with exactly the other recommendation:

“Distilled water is preferable to tap water for use in automotive cooling systems. The minerals and ions typically found in tap water can be corrosive to internal engine components, and can cause a more rapid depletion of the anti-corrosion additives found in most antifreeze formulations.[3]”

And the link pointed to by [3] doesn’t work.

It’ll be great to hear an intelligent answer on this.


There might be some merit to this if he were running straight water in the cooling system.
However, with a mix of the proper antifreeze and water there are additives to prevent corrosion.


A lot has to do with where you live and if you have “hard” water. Hard water has a lot of minerals and if you do frequent coolant changes, as the caller did, every two years, the minerals will build up in the system.

The reference to distilled water being hungry water has more to do with bacteria than it does with minerals. Bacteria fights bacteria. Distilled water exposed to the atmosphere will draw a lot of bacteria out of the air. Water that already has bacteria in it will draw very little bacteria because it already has a balance of bacteria in it.

We have a major water bottling facility near us, that is where I learned of this hungry water theory.

One big error in the brothers theory was the use of flushing, especially using flushing chemicals. Those chemicals do a lot more damage than good. The best thing the caller could do is use a long life antifreeze mixed with distilled water at 2:1 ratio and change it every 5 years.


One of the best solvents is distilled or deionized water. It will dissolve he metals it contacts until it reaches an equilibrium. But once that equilibrium is achieved, it won’t dissolve more. If someone repeatedly changed the coolant and added distilled water, it might be a problem. Most tap water is fine. But well water often has too much dissolved solids which will plate out inisde the coolant system.


The answer may depend on the tap water being used. I had a new water heater put in. Mine was 35 years old. We have Lake Michigan water. The plumber told me it is not unusual to get 20 or 30 years for those on the city watersupply, but those on wells in our area are lucky to get 10 years out of a water heater.


I have heard of this “Hungry Water” theory, and I’ve seen 10X more against it. I worked on an island off shore and we had 3Ga. Distillers for the horrible tap water. One of the guys refused to drink it because he had read that Distilled water would suck the minerals out of your system ! Of course he was about 350 Lbs ! and could stand a bit of Sucking Out. Anyway, I went on-line and found many other articles refuting this claim. After all Water does not have any Power of it’s own unless its moving of course. If that were the case our tape water would be so heavy in metals and minerals we’d have to Ream out our faucets every month !

Need to call this one back for Stump the Chumps.


The coolant fluid used in most internal combustion engines is typically a mixture of glycol (for freeze protection), a pH buffer, corrosion inhibitors and water.

Using distilled or deionized water in the solution is preferred because deposit forming minerals (usually calcium and magnesium compounds, a/k/a “hardness”) and corrosive ions (such as chloride and sulfate) are eliminated. However, distilled or deionized water should not be used as the sole ingredient of the cooling fluid as these are corrosive to many metals commonly used in engines including ferrous metals (iron and steel) and cuprous metals (copper, brass, and bronze).

Depending on the source, “tap” water might be usable. In several areas, municipal source water from surface reservoirs (such as Lake Michigan) has relatively low ion concentration. Although not preferable to using distilled or deionized water, using tap water with total hardness less than 50 mg/l and chloride and sulfate concentrations less than 25 mg/l can usually be done without forming mineral deposits or significantly contributing to corrosion. (Most municipalities now post water quality analyses on the internet.)

Regardless of what water is used, it is important to use a glycol-based product made for the application that includes corrosion inhibitors and a pH buffer. A key point is to get a product that is “made for the application”. For example, using a product that is made for use in a building heating or cooling system (which typically contains an alkaline buffer to maintain the pH in the 9.0 - 10.0 range) in an engine with aluminum components will corrode the aluminum.


I’m sorry, Ray, but this sounds terribly bogus. But to prove it is bogus, we need a carefully controlled study of what gets dissolved in coolant when in use for both tap water and distilled water. Google seems to come up empty.


I think distilled water is recommended mainly because the minerals (Silicas) in tap water could shorten the life of the water pump bearing.

The big cause of corrosion in the cooling system is air getting into the coolant system from a defective pressure cap, loose hose clamps, cracked plastic reservoir tank,etc. Oxygen is considered a very strong oxidizer.

Oxygen that gets into the coolant system on fill up will be taken care of by the additives in the anti freeze, or will oxidize the metals a little, but if the system is air tight the oxygen gets used up, and no further corrosion will take place because the water will become deoxygenated, but if air continually gets in, then the oxygen will over time overwhelm the additives in the antifreeze, and corrosion will continue.

Along with replacing the coolant at manufacture recommended intervals. Making sure the pressure cap is good and the coolant system is air tight is the best way to prevent corrosion.


Hooray for Americar. He got it right. The reference for oxygen being the big corrosion culprit comes from the heating industry. Hot water heating systems are sealed so that no air can enter. One ingredient of the teatment chemicals used is an oxygen scavanger that reduces oxyen to ~ 1 part per billion. They also use distilled water. When pressure caps release liquid to the plastic reservoir that liquid comes in contact with atmospheric oxygen, thus slowly consuming the oxygen scavenger.


Peak site says "Yes, tap water is commonly used for mixing with antifreeze, however, deionized water or distilled water is preferred. Do not use water softened with salts to mix with antifreeze."
It would be interesting to do a poll of shops and see what percentage use distilled water.


I guess there’s several possibilities for what kind of water to use to refill the radiator. Tap water, softened water (if you have a water softener), distilled water, and deionized water. I’ve always used plain tap water. I do get some calcium build up in the radiator, but even on my 1970’s model, it doesn’t seem to affect the ability of the cooling system to keep the engine cooled. I’d hesitate to use anything but tap water unless it was conclusively approved to be less corrosive than plain tap water. I wouldn’t bet my cooling system on a theory.


I think with a radiator that is clogged by mineral deposits (like John’s GMC, and half of the cars in Columbus Ohio)… you should be able to leave the OLD radiator in the car, and use a chemical flush to disolve/remove the deposits. Then put in your distilled water+new antifreeze and save 90% of the repair costs.

If you don’t get the deposits out with a chemical flush, then even after replacing the radiator, you STILL have mineral deposits through the rest of the engine and places like the heater core.

What does anybody think about using CLR for a week, like my post here:


Atlanta_Joe, once significant deposits are formed in the radiator, its EXTREMELY difficult to remove them, no matter what you use. I wouldn’t use CLR because I don’t know what it would do to all the different metals in the engine. If a flush using an automotive-compatible chemical isn’t enough, then it’s time to get a new radiator (assuming it’s plastic/aluminum, like most). If your heater core’s plugged, it’ll also need to be replaced, but that’s not nearly as critical as the radiator.


Passageways inside an engine are a LOT larger than the tubes of a radiator. If we want to change this post to the value of flushes, I will take up a lot of space. Lets stick to distilled water.


The more I think about the ‘hungry water’ idea, the more bogus it gets. Cooling systems typically have problems because of mineral deposits, not because ‘hungry water’ dissolves out things. Leaks are caused by worn components or corrosion, again nothing related to using distilled water. If you wanted to be extra careful, boil the distilled water right before putting it in your car to get rid of most of the dissolved oxygen. But that’s probably overdoing it.


“hungry water” Bogus

Water is an OK solvent. Distilled water will conduct electricity though not as much as water with salts in it. So distilled water doesn’t have minerals, it doesn’t conduct electricity very well. So you basically have no minerals in the water to clog up the radiator, also you don’t have as much worry about dissimilar metals and galvanic corrosion.


I vote for distilled and/or de-ionized water. In both the coolant system and for batteries.

However am disappointed that no one yet has made a connection with Dexcool. Lots of people have had similar problems with GM’s baby Dexcool gelling and blocking passages. No one seems to have questioned the radiator blockage and assumed the diagnosis to be correct as mineral deposits.

Some have nothing but problems with Dexcool while others have no trouble at all. I suspect air getting into coolant system drives Dexcool to gell. Is probably easier to convert to a conventional coolant than to fix an air leak.

Part II; Time once was independent radiator shops stocked raw materials for building radiators. All one needs is an assortment of endcaps and raw radiator panels. If one’s endcaps are still in good shape then new radiator panels could be cut and fitted fairly quickly.


David - are you referring to brass radiators? I didn’t thing the plastic tank/aluminum tube/fin construction could be rebuilt like that.