Why use de-ionised or distilled water in your cosmetic products? Well, because particles and minerals found in tap water may interfere with your formulation and ruin your batches.
Tap water is likely to cause instability in products, as well as affect the shelf life of the finished product . In handmade soaps, tap-water may cause DOS. So, to prevent these unwanted problems, de-ionised water is a necessity and used in all skin and haircare preparations.