Some special diagrams for evaluating the chemical properties of groundwater intended for human consumption are introduced, in accordance with the Italian legislation assimilating EEC Directive 91/271 concerning the treatment of urban waste water and EEC Directive 91/676 related to the protection of waters against contamination by nitrates from agricultural sources. Although the limits imposed by the legislation reflect the Italian situation, they do however conform to directives concerning the whole European Community and offer a response to international guidelines promulgated by, for example, the World Health Organization so they are also suitable for use in national contexts other than Italy. Moreover, a diagram is introduced for monitoring the quality of water destined for agriculture, in particular for irrigation and the special issue of soil protection. In this case, in the absence of specific national and/or European laws and/or Directives, reference was made to the standards of the California Water Quality Control Board. The parameters and the relative limits have been taken from such standards, to identify three quality classes of water for agricultural use with evaluation of use. Plotting such diagrams is very simple: they can be used for improving presentation and interpretation of chemical data and, most of all, to provide comparisons between different water resources or to evaluate possible changes over time. Some examples, reported in the text, will aid understanding their use and interpretation.