Several studies were carried out to optimise rapid tritium analysis in fresh waters by ultra-low background liquid scintillation. These included the optimisation of (i) sample/scintillant ratio, (2) pulse shape analysis, and (3) pulse-amplitude comparator, and studies concerning (1) the combination scintillant/vial and (2) the effect of chemiluminescence. The proposed method involves the mixing of 8 ml sample with 12 ml scintillation cocktail Ultima Gold AB in Zinsser low diffusion vials. These are stored during one day before counting in order to reduce chemiluminescence. The minimum detectable activity achieved was 2.2 Bq·l-1 for a total counting time of 360 minutes. In order to test the method, tritium was determined in Ebro river samples.