This International Standard gives guidance on the selection, and requirements for the application, of ready-to-use methods in water analysis. The so-called "ready-to-use methods" are of increasing interest because, compared to standard methods, they allow fast and often inexpensive results for analytical problems. Under certain conditions these methods can be applied in routine control of water quality, provided they give reliable results. This International Standard deals with practical aspects concerning quantitative ready-to-use methods. Statistical evaluations for establishing the equivalence of ready-to-use methods and standard methods are only mentioned briefly. As the available ready-to-use methods are based on different analytical principles and also show different degrees of accuracy, they are classified into several groups. The aim of this International Standard is to set up criteria as to when the different kinds of ready-to-use methods may be applied for the analysis of distinct parameters in water samples (e.g. potable water, river water, process water, waste water) and which steps are necessary to prove their suitability for a certain application. Ready-to-use methods have to meet special requirements because they are often used by non-chemists. This International Standard lists requirements for the producers of these tests, concerning safety and environmental aspects as well as handling and a description of the procedure. There are also several requirements concerning the training and supervision of the users of ready-to-use methods.