The quality of surface and drinking water depends amongst other parameters also on its content of major components. Many European laboratories therefore routinely monitor such components in rain, surface-, tap-, and drinking water. The need for improvement of the quality of the determinations has led the BCR to produce as a part of a larger project (i.e. project RM 250) two certified reference materials of freshwater with a low mineral content (CRM 398) and a high mineral content (CRM 399). These materials were certified for their contents of Al, Ca, Cl, Fe, Mg, Mn, P, K, Na and S. This project is being continued by the organization of a certification campaign of nitrate in three artificial freshwaters (low, medium and high nitrate contents).