[en] The quality of water in 1 421 drinking-water wells was monitored in a nationwide well water study. Samples were taken once from all wells, and during three seasons from 421 wells. The wells were selected in such a way that me sample would be as representative as possible of the quality of the drinking-water in households' own wells in rural areas. The study comprised general water quality parameters, influence of sampling season, and factors related to the type, the condition and the pollution of the wells. In part of the well waters selenium, radioactivity and pesticides were determined. The effect of plumbing materials on the quality of water was also examined. (33 refs., 148 figs., 71 tabs.)