Ozone is O3 instead of the O2 found in air, and it can give up an atom of oxygen. This results in a very powerful oxidizing agent, toxic to most waterborne microorganisms. After about an hour, it decays back to ordinary oxygen, making the water safe for human consumption and greatly reducing the amount of harmful contaminants in the water. Additional benefits of this type of system are the minimal byproducts, and absence of odor or taste changes. This type of oxidizer can be used to oxidize iron and manganese before filtration. Ozone is created by two methods: corona discharge or ultraviolet light at 185 nanometers. The corona method takes dehumidified air to make O3, or nitric acid will form. Pre-concentrating the O2 in air increases O3 concentration. Systems are sized for total oxidation load. The UV method is commonly used for spa applications.