Is All H2O Equal? Distilled Water Vs Deionised Water

Water is a fundamental part of science, especially Biology in laboratories. If you have ever worked in a lab or have been in one as part of school or university, you will have undoubtedly noticed that in most cases, regular tap water is usually suitable to use for the majority of cleaning. But what about highly sensitive equipment and the experiments themselves?

Certain impurities found in tap water can interfere with the examined chemical processes, making the results from tests inconclusive, or throwing them off altogether. So, if you are working with sensitive equipment, you need the purest water to do so. This then leads to the question, which is better? Distilled or deionised?

In this article, the two are compared, so you can decide which is the best accompaniment for your lab.

What’s The Difference?

When you buy distilled water, it has been cleaned (that is, all of the impurities are removed) via distillation. The water is boiled in one chamber, and then the condensation from the steam is collected in another part of the machine. Once cooled, this water can be used.

Deionised water goes through a chemical process to remove the minerals and ions that could interfere with scientific equipment.

Which is better for your lab? Aren’t they the same? No, they aren’t!

Cleaning Glassware

When it comes to cleaning glassware that has been used in a lab (biological or chemical), you will usually need to use distilled water. This is because it is pure enough to remove all traces of the chemicals or biological materials used, without leaving its own chemical residues.

Equipment Sterilisation

Much as before, in a lab after each experiment, you will need to clean equipment such as microscopes, scalpels and other bits that you may have used. Even if you won’t be using the pieces again the same day, you need to clean them effectively and once again, distilled water is the best way to do this.

 Pure Water? Distilled!

Again, while there may seem to be minimal differences between distilled and deionised water, many labs when they are looking to use pure water for an experiment will use distilled options. This is because (unlike deionised) where the water originated from does not matter, as all of the natural minerals and impurities are removed naturally, without room for chemical errors.


Yes, when you are in a lab, there may be times when you need to cool a test tube down or reduce the temperature of a piece of equipment. For this, deionised water is preferred by many laboratories.

 Final Rinses

As mentioned before, there may be a piece of equipment that you are using in the lab that needs to then be stored away afterwards, which is where a final wash with deionised water can be preferred. Although both distilled and deionised water are ideal for such a process, many labs want to use a liquid that is easier to access (deionised water is cheaper due to how it is created) and will not deposit minerals.

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