A critical assessment of the epidemiologic evidence indicates that a real association between aluminum in drinking water and dementia (including Alzheimer's disease, AD) cannot be dismissed. However, all of the study designs had inherent weaknesses and the results could easily be produced by confounding factors. AD appears to be a multifactorial disease in which multiple genes interact with multiple exogenous factors. Genetic loci for AD have been assigned to chromosomes 14, 19, and 21. Head trauma is a recognized environmental risk factor and aluminum in drinking water possibly is another. Aluminum might accelerate the processes involved in AD pathology. Alternatively, it may act as a neurotoxic agent that has independent dementing effects. The positive findings in the drinking water studies would, therefore, constitute an additive phenomenon. Evidence that aluminum is neurotoxic comes from the exposure during dialysis of patients with chronic renal failure and from the mild neuropsychological deficits reported for aluminum workers. Aluminum bioavailability and mass balance considerations indicate that the contribution from drinking water to the daily gastrointestinal uptake of aluminum may not be insignificant. Since renal disease and perhaps age and AD, as well as natural chelating agents, appear to enhance gastrointestinal aluminum absorption, aluminum in drinking water is considered a public health issue. Even though aluminum is unlikely to be responsible for a major burden of illness from dementia, the level of concern warrants stricter enforcement of the 100 μg/L drinking water guideline used in many jurisdictions. Prudent avoidance by the elderly is recommended of products containing potentially bioavailable quantities of aluminum.Key words: aluminum, Alzheimer's Disease, drinking water, human toxicology, epidemiology, absorption, bioavailability.