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The increase of the nitrate c,oncentration in surface waters used as water supply resources has been investigated with a view to the effects of agricultural activities and atmospheric precipitation. The nitrate concentration increased beyond the acceptable limit for infants after 1975, when due t o the permanent augmentation of the synthetic fertilizer rates the organic humus quantities decreased t o a minimum. The variability of nitrate concentrations in atmospheric precipitation is dependent on the magnitude of precipitation and the intensity of industry in the given region. At a n average value of atmospheric precipitation the nitrogen value in agricultural regions varies within 6 t o 12 kg * ha-I.a-1, in regions with extended industries u p to 24 kgha-l * a-I.