Chlorine gas, the feed rate of which is set at the remote vacuum chlorinator, mixes with the operating water to form a solution which is then fed to a reaction tank. Once the chemicals have fully reacted, the concentrated chlorine dioxide solution is diluted. The quantity of the dilution water is adjusted to give the required strength of the chlorine dioxide. This can be set from 1 up to max. 3 g/l ClO2 depending on the demand. During the filling process the gas produced in the chlorine dioxide storage tank is aspirated by an injector. During off periods, degassing is prevented by an absorber unit. The monitoring functions of the system guarantee the mixing ratio of chlorine gas and sodium chlorite and thereby the virtually full conversion of chlorite to chlorine dioxide.