Metal contaminants in drinking water represent a relevant health issue in several areas of the world. In Italy, because of the geological features of the territory, high arsenic and vanadium are frequently reported in ground waters in concentrations above current guideline values. The implications for public health of the presence of contaminants above their legal limit are directly related to the biological basis of the guideline value. In the case of arsenic there are still major uncertainties in the mechanism of carcinogenesis which prevent a precise evaluation of long-term risks. Thus, the guideline value endorsed in the European Community (10 micro;g/L) has to be considered as a pragmatic tool rather than a quality objective, bearing in mind that "every effort should be made to keep concentrations as low as reasonably possible" (WHO, 2011). A reverse situation holds for vanadium, for which a strict national limit (50 micro;g/L) was previously proposed in consideration of data gaps, and for which new evidence indicated a less stringent health-based limit.