Distilled vs. De-ionized water

[Denis]

Am seeking information about water to be used in cooling systems. Have always used distilled water when flushing and refilling cooling systems. I am well aware of the problems of using "regular" water, especially hard water; scale formation and corrosion because of what's desolved in this type water. I recently read an tech article in a car magazine which stated that the best water to use is de-ionized water and further stated that distilled water leads to much more corrosion and scalling than distilled water. Being curious and puzzled by this , I have contacted the tech people at Zerex, Peak and Prestone and several makers of cooling system anti-corrosion products. When I talked with reps who knew what I was asking; they all told me that de-ionized water was better than distilled water i. e. did a better job of minimizing scale formation and corrosion, and they all told me de-ionized was used in the making of their products. However, no one could tell me why. Any chemists or technical peolpe out there who can shed some light on this??

 

[rholcom2]

I have a question, how do you make de-ionized water. Is it possible to use water that has been through the water softner, and then through a high quality reverse-osmosis system?



Please note this system including the softner cost upwards of $2500, so I consider it to be a high quality system.

 

[nickleinonen]

raw iron will rust quicker in distilled water than in tap water. i accidently tried it in my workshop. i had some drill shavings fall into my dehumidifior's water bucket and some fell into my fresh bucket of cooling water for my grinder/welding cooling. wihin 24 hours, the distilled water shavings were completely rusted, and the tap water ones were still not rusted. .

 

[Denis]

Quick Rusting

Seems to go along with what I was told by the anti-freeze people but the question remains - WHY??

 

[jawmail]

Hi, Deionized(DI) water isn't necessarily any cleaner or better than distilled. There is really really clean DI, almost zero dissolved stuff or there is not so clean DI which might be worse to use than distilled. You can't use the really really clean DI because it will destroy your cooling system. It is so free of dissolved stuff (ions and other things) that everything wants to dissolve back into it, like your radiator. You can get a DI system from an industrial water supply house. They basically look like a water softener with replaceable resin tanks. Distilled is fine for our cooling systems, readily availble and cheap.

 

[Bob Wagner]

jawmail is right on, DI water can be corrosive do to its low hardness content

 

[Denis]

Question

Question to the previous two replies - I thought distilled water was completely free of every dissolved components and was only 100% pure H²O and would therefore has a hardness of 0; wouldn't that would make distilled water very bad to use in a cooling system??

 

[JohnE]

Many "distilling" processes actually put more bad stuff back in the water than where you started.



The condensate from dehumidifiers & A/C units while technically distilled because the dissolved calcium minerals are gone actually has a lot of metallic ions from the coolings coils leaching. De-ionizing is done after a good distilling process to remove the dissolved metals.

 

[jawmail]

Distilled still has things disolved in it but it's still pretty clean so its still fine to use in your cooling system. It's far better than tap water. DI like distilled still has stuff in it to some degree. They measure the purity of water by taking it's resitance to electrical flow. The more pure it is, the higher its resitance. A really pure DI water might have a resistance of 5-15 meg ohms which would make it very pure but also very corrosive. The equipment for a DI system is generally made from 316SS or plastics.

 

[jetenginedoctor]

Truth about water quality

Here’s a topic that I know quite a bit about. It appears that in this discussion, there are actually a few questions:



What’s the difference between DI and distilled water?

What’s the difference between softened water and DI/distilled water?

Why is DI/distilled water corrode metal faster than normal tap water?





I know a bit about water chemistry from my years as a powerplant operator. Water chemistry is extremely critical in any steam plant, especially high pressure and critical pressure plants. We continuously monitor water in all parts of the plant, even including water in the cooling tower which is FAR from being clean!



First off, let’s address what is meant by de-ionized water. The DI process is in some ways similar to how a typical water softener works. A water softener only works to remove minerals that constitute hardness (magnesium and calcium) by forcing water through a resin bed that is saturated with a salt-brine solution. The high concentration of salt in the resin overcomes the lesser concentration of hardness minerals in the water, and replaces the hardness ions with salt ions. This does increase the salinity of the water somewhat, but the salt stays in solution better than does hardness minerals, and are not as hard on pluming, things to be cleaned, etc. Any precipitated salt is much easier to remove than the hardness that would otherwise be there.



Anyway, back to the difference. In a de-ionizing system, water is forced through resin beds that are charged with acid (cation bed) to remove Calcium, Magnesium, Sodium, Potassium, Iron, etc. It then passes through a resin bed charged with a base (anion bed) to remove Bicarbonate Alkalinity, Chloride, Sulfate, Nitrate, Silica and CO2. It then passes through either another cation bed or a mixed bed (cation and anion. ) The effluent is passed through a filter before leaving the process to remove any fractured resins, remaning silica (dirt,) etc.



What you’re left with has been stripped of all ions, and is either H, OH, or H2O. Because there are are no ionized minerals/metals present, the deionized water does tend to ‘attack’ unprotected metals in a given water system. To combat this problem, we used an oxygen scavenger to control corrosion (carbohydrazide,) aqueous ammonia to control pH, phosphates as surfactant, etc. Silica was monitored and controlled by quality of the cycle make-up water, blowing down the boiler drums, etc.



The cooling system is a lot like a boiler with regards to water quality. We hope that there is no localized boiling (prevents convection heat transfer. . . bad juju. ) Localized boiling will deposit minerals on the surfaces against which water is allowed to boil. We hope that the head pressure of the water pump combined with the overall system pressure held by the radiator pressure cap is enough to sufficiently raise the boiling point of the coolant high enough to allow the cooling system to do its job. Just like in a boiler, we don’t merely use pure water. Though pure water will prevent hardness deposits on the heat transfer surfaces, it will not prevent actual corrosion. Antifreeze products add to the situation surfactants, seal lubricants, and corrosion inhibitors that are very important if you wish to have an efficient cooling system with longevity. Guys who run straight water are making a mistake. If they’re using tap water, they’re fouling their cooling system with hardness minerals. If they’re using distilled, DI water, or RO water, they’re encouraging corrosion.



So, what’s the best water to use? Because of the energy involved in PROPERLY distilling water for purification, I’d be willing to say that the water we buy at the grocery store is probably NOT really pure. Most RO systems likewise will not remove 100% of TDS. Softened water??? Not in my cooling system. . . no way. The solids that are likely to be present in any RO, DI, or distilled water is negligible in a cooling system so long as a quality coolant is used. I really think that saying one is ultimately better than the other is like splitting hairs. The quality of water you get at the store is not a constant. Consider the fact that there are a lot of volatized organics leached into the water by the containers they use, and it really kindof throws a hammer in the cookie dough.



Whatever you do, don’t use tap water, “spring water,” drinking water, etc. If it says distilled or no-sodium, processed by reverse osmosis, you’ll be okay. Just make sure you use a quality antifreeze.



BK

 

[Bob Wagner]

BK, good post and welcome to the TDR

 

[Denis]

Thanks

BK

Thanks for the info.

Denis

 

[PPettit]

BK, great explaination! I just wanted to emphasize that using DI water should cause no corrosion problems in your system as long as you use good anti-freeze. I have been using 18Meg DI for cooling systems for many years now.

Do you suppose there would be any merit in putting straight DI in your system to try and remove scale from an older engine?



Phil

 

[lschultz]

BK come on over to our utility plant and you can take care of our boilers and cooling towers. You might do a better job than our 2nd shift fellows do. I shouldn't say that they only put in what Nalco tells em. Our cooling towers looks like **** lots of alage on it.

 

[jetenginedoctor]

BK, great explaination! I just wanted to emphasize that using DI water should cause no corrosion problems in your system as long as you use good anti-freeze. I have been using 18Meg DI for cooling systems for many years now.

Do you suppose there would be any merit in putting straight DI in your system to try and remove scale from an older engine?



Phil

The only way to remove that scale is by raising the pH to around 10 and keep it there. I wouldn't recommend doing that, though. If there's scale in a radiator, it can be boiled/rodded out in a vat of caustic soda with little drama. Sadly, the same thing isn't true of an engine block. That's why it is IMPERITIVE that you never put anything other than demin/distilled water and coolant in a cooling system. This means no stop-leak BS, etc. Anything that adds solids to a cooling system WILL have a detrimental effect on system efficiency. This can even include some of the corrosion inhibitor additives that guys will use (mostly in CA, AZ, NM) with straight water when they think coolant is money wasted. They're wrong. Corrosion inhibitors will boil out of solution and precipitate on the heat transfer surfaces just like hardness minerals will.



If you somehow find yourself stranded in the middle of BFE with an empty cooling system, and tap water is the only thing available, then use it. But as soon as you're somewhere that you can drain and flush the system with demin/distilled/RO water, don't waste time. The longer you run with tap water in the cooling system, the more damage you're doing.



BK

 

[jetenginedoctor]

BK come on over to our utility plant and you can take care of our boilers and cooling towers. You might do a better job than our 2nd shift fellows do. I shouldn't say that they only put in what Nalco tells em. Our cooling towers looks like **** lots of alage on it.

It's not uncommon to have some algea growth in a cooling tower. Depending on what your discharge permit allows in terms of chorine emissions, you might have to shock the tower with a bit more bleach. Not sure if you're neutralizing the discharge of the cooling tower or not. We were supposedly a "Zero Discharge Plant" (yeah, right) so we had to remove 100% of the chlorine from our cooling tower blowdown. That meant keeping a close eye on cycles of concentration, chlorine, etc. We had a system that automatically nuetralized the chlorine in the blowdown from the CT, and a monitor that would sound an alarm if we started blowing down anything above our permitted chlorine level.



ANYWAY, when our plant was built, we hired some chemist to come create a boiler chemistry program for us. What an idiot. We had a couple real boiler water chemists working at the plant that quickly squared things away after he was gone. Our chemical supplier was Betz/Dearborn (GE/Betz now. ) Every one of the operators had to go to school to learn about boiler water chemistry. It was pretty interesting, has a lot of applications outside of the powerplant.



I wonder how many other plant operators read this forum?



BK

 

[opjohnny]

Sounds like a good reason to go with the premix stuff even though it is more expensive. If your just topping off the overflow tank.

 

[jimk]

I also work at a coal fired power plant, there is a water treatment plant to supply good water to the boiler. Water treatment is part of our area. I got tired of nights so maintaince is best for me. I have worked both operations and maintaince. I have used the water from the Lab in my truck for years and it is doing fine.

After 17 years you would think that you have heard and seen everthing but they just keep supprising us with new BS all of the time. O well the pay is good Jim