Previous studies in this series of papers investigated the associations between aluminum (Al) water concentrations and relatively high risks of a measure of mental impairment and also various possible other drinking water characteristics, particularly pH, turbidity, fluoride and silica. The results were based on one measure of mental impairment, which would not be expected to give the same results as the more definitive endpoint (outcome variable) of a record of Alzheimer's Disease (AD) as the underlying cause of death on a death certificate. The present paper therefore investigates the relevant associations, based both on the measure of mental impairment and on death certificates in which AD and presenile dementia are listed as the underlying causes of death. As expected, the associations were not identical, but they were similar. More specifically, Al water concentrations were strongly associated with the recording of AD on death certificates, as were pH, fluoride, and silica concentrations. The implications of these results are discussed, and it is suggested that the evidence is sufficiently strong for methods of water purification to be modified, at least on a trial basis, because of the likelihood that this will reduce the incidence of AD.

Previous papers reported on the associations between water quality and a measure of cognitive impairment, based on data of the Ontario Longitudinal Study of Aging (LSA). The present report summarizes the information on fluoride (F) and aluminum (Al) and provides additional information on the effects of pH. Specifically, our preliminary results suggest that a neutral pH, relatively low Al and relatively high F concentrations in drinking water decrease the odds of showing indications of cognitive impairment by a factor of about five, compared with other types of drinking water. The relevant chemical reaction is ascribed to an equilibrium involving Al complexes.