The difference between demineralised and distilled water

Lots of people confuse distilled water with demineralised water. No surprise, even the names are similar. Yet the two types of water really are different. Demineralised water is generally slightly less pure than a distillate. In this article, I'll explain why.

Distilled water

Distilled water is heated to boiling point. The condensation (steam) that comes off it is then collected. This leaves almost all the substances that were in the water behind, so you're left with only the pure water.

So this type of water is incredibly pure and is used, for example, in hospitals or the food industry. Basically in places where the water absolutely must not be contaminated. Sometimes demineralised water is chosen anyway, because it's cheaper.

Demineralised water

Demineralised water, or demi water for short, has been filtered. By filtering tap water, you remove the negative ions from the salt, leaving only positive ions. So this form of water is clean and clear, but not completely pure.

The (tap) water being filtered runs over an ion exchanger, which replaces unwanted substances (cations and anions) with an equivalent amount of other ions. It's important that the exchanged ions have the same charge so the water stays neutral. Basically, all particles larger than the water molecules are held back by the filter.

The process is quite tricky, but in the end it gives us clean water with a neutral pH that no longer contains minerals. But it's definitely not as pure as the evaporated liquid of distilled water. This is because of the ion exchanger: after a while algae can start to grow in it, which means it's actually impossible to work 100% sterile.

In principle you can filter tap water yourself, but it doesn't always lead to the very best results. You can buy a special filter for this. Still, it's wise to call in an expert or buy ready-made bottles of demineralised water if you don't need it often.

Demineralised water is mainly used in laboratories and personal care products. When you apply products to your body, you want to do so with pure water that isn't full of unnecessary contaminants, as these can irritate your skin. Impure water also encourages bacterial growth, which is very inconvenient if you want to make your own cosmetics.

Demineralised water is drinkable in principle, but it comes with both pros and cons. It simply no longer contains any minerals, so it isn't meant as a replacement for regular drinking water.

In short: both waters are very clean, but a distillate is extra pure and is therefore often used for medical purposes. So depending on what you need it for, you use either distilled or demineralised water. If you want to make your own cosmetics, demineralised water works perfectly well.

Author: Aurelie Deloo