Objective To study the variations of microorganism indexes of barrelled purified water during its preservation period of 90 days. Methods The total count of bacteria, the mould and yeast count, the conductance rate and pH value in water samples collected from the fresh products of barrelled purified water at the same day of production and then at the 5th, 10th, 20th, 40th, 60th and 90th days after the production date respectively were determined. Results The total count of bacteria of barrelled purified water reached peak at the 5th and 20th days during the observed preservation periods, and then decreased gradually. No significant variations of mould and yeast count, decrease of pH value (6.3 to 6.0), increase of conductance rate (4.2 to 5.8 ?s/cm) were observed in the barrelled purified water during the whole 90_day preservation period. Conclusion The total count of bacteria of barrelled purified water was fluctuated obviously in the observation period. A suggestion was made that the time limit of quality guarantee for preservation period of barrelled purified water must be within 30 days.