The rural population, estimated at one third of Lithuania's population, obtains drinking water from shallow wells. Drinking water from shallow wells is polluted, for the most part, with nitrate, which is of general concern not only in Lithuania but in other countries. The purpose of our study is to establish the relationship of nitrate pollution in the water of shallow wells to precipitation level and temperature, as well as to assess the impact of well construction and environmental conditions on this kind of pollution. The results of this work showed that about 66% of all investigated wells are nitrate polluted. The results of long-term research have demonstrated that the highest nitrate concentration in the water of shallow wells occurs in March through July, and the lowest nitrate concentration in September through February. A strong correlation between nitrate concentration, precipitation amount and air temperature was established in summer. Correlations established in other seasons are not significant. The strongest impact on nitrate pollution of the wells is related to the distances of the well to the outhouse, cowshed, manure pile and vegetable garden, as well as the surroundings of the well and local human activities. The estimated coefficients of multiple linear regression allow forecasting the nitrate pollution of the wells as a function of these factors.