The efficiency of a water treatment or a water monitoring program can be checked only if it is accompanied by water analysis procedures allowing meaningful statements on water quality. Meaningful statements do not only include high accuracy, but as well high precision. With high precision values, good repeatability and reproducibility is aimed for. Repeatability and reproducibility may either be monitored by regular interlaboratory trials without prescribing a distinct analytical method, or by applying a standardized method which has undergone thorough check concerning its reliability and efficiency. History and development of International and European standards is shown and the relationship between both - and the national standardization as a root - is given. If it is possible to continue in the reported way of close cooperation, double work or contradictory work will be avoided. Work on standardization in the field of water protection will be continued.