The paper describes the method, recommended by the Quality Assurance Committee of the European-African Group of the International Ozone Association, for the determination of the ozone demand of a water. For that laboratory test, ozone can be injected as a gas, or as a solution of ozone in water. The paper delineates the main analyses of the water which are needed to characterize the water, and as well as the framework of presentation of the results: table and graph.