Due to inherent methodological limitations in ecological studies like the present one, causal interpretations should be made with great care. Thus, although the results give some support to the hypothesis that drinking water chlorination is associated with colorectal cancer, they do not provide strong evidence of a causal relationship. Title Chlorination of drinking water and cancer incidence. Different studies appeared to lend some support to the hypothesis that surface waters contain higher levels of human carcinogens than groundwater sources. The possible contaminants that might play such a role are the halogenated organic compounds produced by the chemical reaction between organic materials in water and chlorine used for disinfection.
Chlorine reacts with naturally occurring organic compounds in the water to form haloforms.
Valencia Province of Spain relies almost exclusively on groundwater for its public drinking water, but the city and surrounding urban areas rely on superficial water. To find an association between stomach and bladder cancer mortality with the type of water source, we studied 261 municipalities of Valencia Province. Title Pilot study on the relationship between male stomach and liver cancer death and mutagenicity of drinking water in the Huangpu River area. Total person-years observed are 184,645. It suggests that a causal correlation may exist between the two.