Deionized Water vs Distilled Water for Heat Transfer Applications

Heat transfer fluids are often diluted with water to achieve the appropriate freeze protection required, and sometimes systems are filled with water alone. Which type of water should be used- deionized water or distilled water?

Deionized Water

Deionized water is produced by running water through an RO unit, resin bed system, or some similar piece of equipment. This purification process, sometimes referred to as ‘water polishing’, will strip out most impurities and ions in the water, but will leave some essential ions behind. This water is a good choice for using in heat transfer applications, because the impurities have been removed, but some essential ions are still present, which makes it less corrosive. When using deionized water for heat transfer applications, there are no issues with compromising the system, the integrity of the materials, the construction or any heat transfer fluid that may be used. Standard inhibitors can be used. It is also less costly to manufacture deionized water.

Distilled Water

When water is distilled, ALL impurities and ions are completely stripped out of it. Distilled water is truly pure water. However, it is also very ‘hungry’ for some essential ions that it is now lacking. The water will try to pull the necessary ions out of anything it comes into contact with, making it extremely corrosive. Although we don’t recommend using distilled water for heat transfer applications, it can be used, if it is used with the correct inhibitor package. This may mean that a bolstered inhibitor package will be necessary over a standard inhibitor package. If it is used without the correct inhibitor package, it will seek out the ions that it is ‘hungry’ for from the materials and construction in that system and it will begin to erode the system. Distilled water is also more expensive to manufacture. As a result, CORECHEM generally does not blend distilled water with our heat transfer fluids unless by special request.

With other questions about what type of water you should use in a heat transfer application, reach out to a heat transfer specialist today! Or, browse our heat transfer fluids here.