We have previously reported on the ubiquitous presence of perchlorate in the deposited and airborne fine dusts of Malta and shown that the source of the chemical in the dusts of this small central Mediterranean island is fireworks. There are no local geologic or anthropogenic sources of perchlorate other than firework manufacture and display. The hypothesis was tested that ground-deposited perchlorate will be mobilized in runoff and would partly migrate to the water table and eventually also affect tap water, one third of which being derived from groundwater. Forty four percent of 36 groundwater samples contained perchlorate above detection limit with mean and median values of 1.09 and 1.1 μg L-1. Sixty-two percent of 16 runoff samples collected during storms contained perchlorate above detection limit with mean and maximum concentrations, respectively, of 50.8 and 129 μg L-1, values which are far too high to be explained by atmospheric inputs given that rainwater perchlorate levels are typically <3 μg L-1. Between 42 and 89% of the tap waters analyzed in three sampling campaigns contained perchlorate above detection limit and had mean concentrations ranging from 0.4 to 1.6 μg L-1 suggesting contamination levels similar to those reported from China but lower than levels reported from the USA. The phenomenon of contamination of the water resources of Malta by perchlorate is probably unique in that it results not from geologic or industrial inputs but from an intense and prolonged pyrotechnic activity that is deeply rooted in the popular culture of the islanders.