The Differences between Distilled Water and Deionized Water

Distilled VS Deionized Water

Tap water may be the most ordinary water in our daily life. Of course, you can drink it directly, if the tap water smells and tastes well. If not, you may need a water filter or water distiller to purify water first. However, for most laboratory tests, calibrating equipment, preparing solutions or cleaning glassware, tap water is not suitable because there are some impurities in the tap water. The most suitable type of water for the lab is purified water. Most common methods that are used to purify water include distillation, deionization and reverse osmosis (RO).

Deionization and distillation are similar to each other. Both of them can remove impurities. However, essentially deionized water and distilled water are different. And they cannot be interchanged for most lab tests or purposes.

In order to understand their differences, first we need to how deionization and distillation work. After that, we can understand which one is the best type of water for your lab purposes or when it is OK to interchange one for the other.

How Distilled Water Works

distillationEssentially, distilled water is one type of demineralized water which is purified by distillation. You can use tap water to make distilled water, and you also can use spring water to make it. The source water is boiled in a container, and the steam arises and will be collected and condensed to get distilled water. The whole distilling process is called distillation. During this process, most minerals and impurities cannot rise with steam, so they are left behind. However, some volatile organics, mercury, as well as other impurities also rises together with steam. Therefore, how pure of your source water can influence the purity of the resulting water. Most home water distillers even use a post-filter to remove these VOCs in the steam. At least, distillation can remove most particulates and salts. To make distilled water, spring water is better than tap water.

How Deionized Water Works

deionizationDeionized water is produced by running spring water, distilled water or tap water through an electrically charged resin. The key part is the mixed ion exchange bed which has both negative and positive charged resins. It is known that salts are made up of cations and anions which are free ions. The H+ and OH- ions in the reins will exchange cations and anions in the water, resulting in H2O (water). During this process, salts are replaced and removed. However, deionized water is very reactive. Once it is exposed to air, its pH will changes from originally 7 to 5.6, because it will dissolve CO2 in the air and finally form carbonic acid solution. However, deionization only remove salts and will not remove molecular specials or uncharged organic particles, because these matters don’t have free irons in the water.

Distilled VS Deionized Water in the Lab

As we mentioned before, the purity of source water will affect the quality of distilled water. Generally, tap water or spring water is considered as the most suitable water to make distilled water. Here, let’s assume the source water was spring water or tap water, so distilled water is pure enough, making it suitable for almost all lab applications, including:

  • analytical blank
  • calibration standard
  • cleaning glassware
  • equipment sterilization
  • making high purity water
  • solvent to prepare solution

Similar to distilled water, the purity of deionized water also is influenced by the source water. And deionized water is used if a soft solvent is required, including:

  • analytical blanks
  • calibration standards
  • cooling applications
  • microbiology autoclaves
  • many chemistry experiments involving ionic compounds
  • washing glassware, especially the final rinse
  • solvent preparation
  • in batteries

In a word, in some situations both deionized water and distilled water are suitable for use. However, because deionized water is more reactive and corrosive, it is not suitable for situations that involve long term contacting with metal.

Substituting Distilled and Deionized Water

Generally, it is not recommended t substitute one for the other one. However, if your deionized water is made from distilled water, it is ok to substitute the deionized water for the distilled water. All in all, you should know the one you use to substitute for the other will not influence the result or outcome. The safest way is not to substitute one for the other.

Drinking Distilled Water or Deionized Water

Some people think their water is very dirty, so they use home water distillers to make distilled water and drink it every day. However, this is not the best choice because distilled water lacks minerals found in tap water or spring water. Therefore, it is recommended not to drink distilled water for a long time.

Of course, drinking distilled water not for a long time is no problem, but deionized water is not suitable for drinking. Deionized water also lacks minerals. What’s worse, it is corrosive, so it can cause damage to our tooth enamel and other soft tissues. And, deionized water may also cause infectious diseases because deionization cannot remove pathogens.

The bottom line

You can drink distilled water and deionized water, but you need to make it exposed to air for a while and the quality of the source water should not be poor.

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