ABSTRACT: Agriculture is the main source of groundwater pollution by nitrate. This is a result of the rising use of synthetic nitrogen fertilisers and the increasing consumption of animal protein by the population in developed countries. Nitrate is not a component of rock minerals or soil particles; it is a product of nitrogen turnover in soil with short live time. Once nitrate appears in soil, it is quickly absorbed by growing plants or bacteria to form new organic substances. The nitrate concentration in cropped soils varies greatly during the hydrological year and is at its highest in late autumn, when the main volume of water is percolating to the saturated zone. The observed and calculated data show that, in lowland Poland, the annual leaching rarely exceeds 25 kg ha-la-1 NO3-N. Such leaching, and higher, is likely to occur on sandy soils, prevailing in Poland. The best way to mitigate the groundwater pollution by nitrate from agricultural sources is through the implementation of Best Agricultural Management Practices and the effective education of farmers and rural area population.