The tritium level of the precipitation in Korea is monitored at the Pohang Station from 1961 to 1976 and at the KAERI from 1981 to 1994. The tritium contents of the precipitation were recorded to about 1,300TU owing to world-wide nuclear devices in 1963. The tritium contents of precipitation, surface water, groundwater, and sea water in 1991 are 10TU, 14TU, 15TU, and 4TU, respectively. The tritium content tends to increase from Cheju Island (14TU) to Baekdu Mt. (48TU). This shows that the tritium contents increase with latitude and are effected by the altitude. The tritium contents of surface water, groundwater, and discharged water from heavy water-type nuclear power plant are measured higher than natural level. The tritium contents of discharged water from the fracture zone of the horizontal tunnel in the Chungyang area are analyzed. The data of tritium contents are applied to dating of groundwater by PFM and EM. The tritium contents of precipitation monitored were available as input data for dating of groundwater. Results of dating of groundwater are from about 14 year to 20 years.