Topics outlined in an earlier paper by Eichhorn are expanded, with particular emphasis on the implications of the associations between aluminum (Al) concentrations and various indications of mental impairment. These associations represent the main thrust of the evidence that Al is a contributory cause for some forms of dementia. Of particular interest are the more recently observed associations between Al concentrations in drinking (finished) water and various indications of mental impairment, and the relevance of other water quality variables such as silica, fluoride, and pH. Various unresolved questions are also identified.