Much like in a swimming pool, sanitation or disinfection plays a crucial role in spas to treat bacteria. The combination of heavy use and hot water places a tremendous burden on the sanitiser used. Whatever the source, all of the billions of micro-organisms present in a spa need to be killed in some way and as quickly as possible. To do this, a sanitiser must be continually present in the water in a measurable residual amount. Whilst other sanitiser options are available, chlorine and bromine are the two main chemicals recognised by Health Authorities as providing the necessary level of safety for bathers.