A survey to study natural radioactivity in drinking water was carried out in Catalonia (northeast Spain). Approximately 800 samples of drinking water were analysed between 1986 and 1993. The samples were categorized according to origin: bottled or public supply. The samples were analysed for gross alpha, gross beta, 234U, 235U, 238U, 226Ra, 228Ra, 230Th, 232Th, 210Pb, and 210Po activity. The activity concentration for gross alpha was found to range from 0.02 to 1.75 Bq/L and for gross beta from 0.04 to 2.9 Bq/L. The gross beta activity content in the majority of the samples is due to 40K. Average concentrations of 234U, 238U, 226Ra, and 210Pb in the waters studied ranged from 10 to 100 mBq/L. Concentrations of 700 mBq/L were obtained for 234U, 960 mBq/L for226 Ra, and 1130 mBq/L for 210Pb. The highest levels of alpha radioactivity are due to the presence of granitic formations in the region. A high degree of radioactive disequilibrium was noted among members of the uranium series present in some samples of water. The 234U238U activity ratio varied between 1 and 4, and the waters with the lowest uranium activity registered the highest level of 234U238U activity ratio.