The Directive on the Quality of Surface Water Intended for Drinking Water defines three categories of water treatment (A1, A2, A3) from simple physical treatment and disinfection to intensive physical and chemical treatment. The treatment to be used depends on the quality of the water abstracted. The Directive uses imperative values for parameters known to have an adverse effect on health and also guide values for those which are less adverse. There is also a directive which complements the "surface water abstraction" Directive by indicating the methods of measurement and the frequency of sampling and analysis required.