For search terms, we used combinations of the key words "health," "water," and "radioactivity." The word "health" was alternatively replaced by "epidemiology," "case control," "cohort," and "cancer." The word "radioactivity" was alternatively replaced by the names of the elements occurring in the decay chains of interest, namely uranium, thorium,
protactinium, actinium, polonium, bismuth, radon, thallium, and lead.