Water is the basic constituent of all living beings; it is, therefore, an essential dietary element and a primary resource. The D. Lgs. 31/2001 is the Italian standard reference concerning drinking-water issues. The purpose of this article is, firstly, to highlight that chlorination, as a water purifying treatment, does not guarantee an absolute absence of risk. On the contrary, it causes the formation of various by-products, many of which are known to be carcinogenic and mutagenic. Secondly, some drinking-water pollutants have mutagenic and carcinogenic properties, giving an appreciable risk for the user. As a result, water reserves, because of their importance to public health, should be properly safeguarded and protected to prevent possible contamination. Although disinfection brings about mutagenic and carcinogenic molecules, we cannot do without it if we want to prevent the much more severe risks due to the presence of pathogens in water used for human consumption.