Disinfection of the pool water aims to stopping microbiological activity and destruction of microorganisms. Disinfection is not, however, sterilization, because some of these organisms can survive in inactive state eg. by creating spores, which do not grow and not multiply, but exist. As soon as the ambient conditions will become favorable, the spores re-adopt its active state and can rapidly multiply. Therefore, disinfection must be conducted continuously. The products are used in concentration, which is toxic to microorganisms, not to humans Normal conditions for good disinfection is: 0,5 to 1,0 mg/l of chlorine, pH between 7,20-7,6.