ABSTRACT
This chapter describes microbiological and chemical risks encountered in drinking water and discusses their control and relative importance. The drinking water supply can introduce contaminants such as disinfection chemicals or their by-products and materials such as those from pipes, which may elute chemicals. The World Health Organization (WHO) guideline values for chemicals were calculated separately for individual substances without specific consideration of the potential for interaction of each substance with other compounds present in the water supply or with microbiological contaminants. The WHO drinking water quality guidelines incorporate values for 14 genotoxic carcinogens. Both groundwaters and treated surface waters are normally subjected to disinfection before distribution. Chemical disinfection employs substances that inevitably react with other chemicals in the water as well as with the microbes they are intended to kill or inactivate. Various types of cancer are the diseases of concern in relation to disinfection by-products, although the evidence for carcinogenicity of disinfected drinking water is inadequate.
