What is Deionized Water and why does it matter? Unless you’re a scientist working on isolating ions in a lab, you may not be aware that there are many different types of water and each has different properties. While purity and mineral content are considerations in drinking water, there’s more to consider when using water in cosmetic formulations. The science behind why we use deionized water is pretty cool, but let’s start with the most common types of water used in cosmetic formulations.
City Water/Tap Water
Straight from the tap, water from municipal water sources contains many small metal and mineral ions. It also contains a variety of synthetic and natural chemicals used to treat the water making safe to drink. The different ions give the water its flavor, but they can also react with ingredients in your cosmetic formulations. We don’t recommend using straight tap water when making your own cosmetic formulations. The ions can make your emulsions more difficult and they may even affect the color of your final product. We’re pretty fortunate here in Portland as our tap water comes directly from the Bull Run Water Shed. It’s a protected, clean water source and absolutely delicious to drink, but still full of metal and mineral ions.
Distilled Water
Distilled water is made by boiling water in a still, collecting the steam, and condensing that steam back into water. This process removes salts and particulates except those that boil at a temperature lower than water. For this reason, the source water is important as any contaminants, such as mercury and volatile organic compounds, that boil at a lower temperature than water will remain as the steam is condensed back into water. Distillation will leave most mineral ions behind making it similar to deionized water, but not the same. If you are confident that the source water used is pure, distilled water can be used in your formulations but if you have undesireable results, consider using deionized water instead.
Demineralized Water
This is water that is passed through an ion-exchange filter to remove salt ions. It’s defined as any water that has had the minerals removed so technically deionized water is demineralized water.
Ultra-Pure Water
When you absolutely, positively need absolutely pure H2O, you need ultra-pure water. The water is first demineralized and then is passed through an electro-deionization process. The main use for this type of water is in pharmaceutical applications and electronics. It’s expensive and probably overkill for most applications and therefore unusual to see this used for cosmetics, however, it’s pretty interesting.
Simply put, deionized water is water that has all ions removed. You may be thinking “What about oxygen and hydrogen”? Without getting too scientific, once oxygen and hydrogen form a covalent bond to make water they are no longer ionized…..except to a tiny degree (but we won’t go too far down this rabbit hole). Deionized water removes the ions, but does not remove any other impurities, so if the water you deionize is full of bacteria or viruses they will remain in your water.
Which Water does Essential Use?
We have an in house deionized/water purification system. Water from our city water source, the Bull Run Watershed, is passed through resin beds to remove ions, it is then passed through a 2 micron filter, passed through another set of resin beds to ensure all ions are removed, passed through a one micron filter, passed through a UV light box, and finally through a 0.5 micron filter. Whew…..that’s a lot of filtering, and there are reasons we make sure the water we use is deionized and pure. Using purified water ensures that there are no unwanted contaminants, but the real magic is in using deionized water.
- Emulsions – Using deionized water makes emulsions more stable. Whether it is an oil in water or water in oil emulsion, having water that is “hungry” for ions will help your emulsion remain smooth and stable
- Ingredient reactions – some ingredients will react with ions in water in unwanted ways. For example, kojic acid will react with iron ions turning a distasteful brown color.
Water isn’t as simple as it seems, at least when it comes to using it in cosmetic formulations. Take the guess work out of your formulation and start with Deionized Water. It will most likely save you time and effort in the long run.
