In most water treatment plants ozone is used for multiple applications. Ozone is now used as a disinfectant, an oxidant of organic and inorganic molecules, a coagulant aid, removing taste and odour, a means of controlling algae and as a way of biologically stabilising water. Ozone is very effective for disinfection against bacteria, viruses and protozoa. However, when used in a disinfection capacity, it is often used when contaminants are highly resistant to more conventional disinfectants.