Abstract The method specified is applicable to all types of water including seawater with concentrations of up to 10 ^ 6 Bq/m ^ 3 when using 20 ml counting vials. The method is not applicable to the analysis of organically bound tritium; its determination requires an oxidative digestion. The choice of the analytical procedure, either with or without distillation of the water sample prior to determination, depends on the aim of the measurement and the sample characteristics. Direct measurement of a raw water sample using liquid scintillation counting has to consider the potential presence of other beta emitter radionuclides. To avoid interference with these radionuclides when they are detected, the quantification of tritium will be performed following the sample treatment by distillation. Three distillation procedures are described. The method is not applicable to the analysis of organically bound tritium; its determination requires additional chemical processing (such as chemical oxidation or combustion). With suitable technical conditions, the detection limit may be as low as 1 Bq l-1. Tritium activity concentrations below 106 Bq l-1 can be determined without any sample dilution. A prior enrichment step can significantly lower the limit of detection.