When formulating at my previous company, the type of water used was never something I thought about much. In the lab, we had a benchtop water deionizer and used it whenever making aqueous formulas. Of course, not everyone has one of these devices and there are other water options you should know about. The different types of water used in formulating cosmetics include tap, distilled, deionized, and purified) water. Here are some water type definitions.
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Tap water
Tap water comes from municipalities and is suitable for many types of cosmetic products. But when you get the water right from the city water supply, it’s filled with a small amount of metal and mineral ions. Often this will not have any effect on your cosmetic formula, but it can be a problem especially if you are using any soap-based ingredient. Since this type of water doesn't allow you to control the level of ions in the formula, it’s best to use something that is more purified.
Distilled water
Distilling is the oldest method for purifying water. In this process water is boiled in a still. The vapor is collected in a condenser and cooled to reform the water. Theoretically, it removes all traces of contaminants except those that boil at a temperature lower than water, such as some alcohols. It also will absorb Carbon Dioxide from the air so the pH will typically be lower (pH 4.5 – 5.0). This is suitable for most any type of formulation but can be inconvenient if you have to produce it.
Deionized water
This is water in which the non-water related ions have been removed. Tap water is usually filled with ions from the soil including sodium, calcium & magnesium plus metal ions from the pipes such as iron and copper. It is deionized by sending it through an ion exchange column, which is a tube that contains a resin that selectively binds with ions in water. Ionized water goes in and deionized water comes out. This process doesn’t remove organic contaminants, viruses or bacteria. This water is suitable for most any formulation and can be produced quickly.
Demineralized water
This water is sent through an ion exchange process and is pretty much the same as deionized water. From a formulation standpoint, there is no difference.
Ultrapure water
When you want just pure H2O, this is what you want. The water is first demineralized, then sent through an electrodeionization process. This is great for electronics and pharmaceuticals. It’s probably over-kill for cosmetics.
There you have it, all the different water types you might use when making cosmetic formulas. One final note: no matter which type of water you use when making a cosmetic, the only proper way to list it is on the ingredient list is WATER or AQUA.
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Fully agree on the water specifications, in our plant, I’m using several kinds of water depending on the category of products. I’m working in the plant since 24 years, and I’m spending a lot on testing the water, Analytical and Micro.
What about Reverse Osmosis?
The few cosmetic facilities with which I have been involved have all had water purification systems that have had a deioniser, a carbon filter (to remove organics) and reverse osmosis in sequence.
Or is that becoming unfashionable nowadays?
From a microbiolgical point of view, tap water in no way is a good solution – unless you filter it through a 0,45 microns cartridge (0,22 even better). Of course, you must remove all colloids and free chlorine before, so more filtration steps are required to send tap water to the manufacturing. Very best is reverse osmosis, whose only limit is the size of the plant if you design it on the maximum water request; this bottleneck is usually overcome by a suitable storage tank. In ISO 22716 special attention is paid to water: we must remember that most of cosmetics products have a water content more than 50%, to reach 95% too. Of course an ingredient of so great weight requires a special care in manufacturing and controls. Lowering the price of reverse osmosis membranes have driven a change in plants: until some years ago the first step after removal of colloids and chlorine from tap water was the deionization (allowing a better yield in permeate), while now the first step is reverse osmosis, refined by deionization to a water of high purity. Immediately before the point of use of the purified water, usually a cartridge filter 0,22 micron to ensure microbiological purity. Usually after the deionization step a 2-5 micron filter is required, to stop particulate and powder from resins degradation before they can reach the 0,22 filter.
Another benefit of using purified water, be it produced by distillation, deionisation or reverse osmosis is that you have no variation (or very little variation) in the quality of the water, which results in a more consistent product quality. While tap water is generally very low in microbiological contaminants, due to the addition of Chlorine, the downside to tap water is that the traces of impurities can react with other constituents in formulations and it is less consistent when analysed.
I would add that there are slight differences betweeen deionised and demineralised water, namely that deionised is free of ions, while demineralised is free of minerals https://www.chemicals.co.uk/blog/is-demineralised-water-same-as-deionised-water
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