Good 'ol H20! Aqua is the name for water that has been purified to remove any impurities such as bacteria, organic compounds like minerals, or enzymes. This type of water is used throughout many products in all sorts of industries such as body care, hair care, skin care, pharmaceutical, automotive, and laboratory testing. We use this type of water specifically as the presence of minerals or other substances can cause problems in the finished products. We also recommend using distilled water in diffusers as it can help prevent mold and bacteria build up and prevent any residue from normal water from forming in the diffuser which, over time, could cause the diffuser to clog or break.