The Polish Geological Institute has been carrying out the tasks of the geological survey since its establishment in 1919. Hydrogeology was present from the very beginning and the groundwater monitoring became the systematic activity in the 2nd fifty years of the Institute’s life. Groundwater quantity monitoring expressed as measurements of groundwater table fluctuations was put into practice in 1972, while the groundwater quality monitoring that includes determination of chemical composition of water started in 1991. Both types of monitoring cover the entire area of Poland. Systematic hydrogeological observations and tests are one of the most important tasks carried out by hydrogeologists of the Polish Geological Institute. Results of these observations are used for many studies, analyses and forecasts carried out as part of the tasks of the hydrogeological survey, often in cooperation with universities and geological enterprises, for the needs of governmental and local administration and for reporting to the EU structures.