Design The study was done in two stages. Firstly water samples were taken daily from the reservoirs of 20 autoclaves used in general dental practices for six days. The microbial content and endotoxin concentration was determined. Second the practitioners were instructed to wash and clean the reservoirs of the autoclaves each morning prior to refilling with fresh water. The reservoirs were sampled in the evenings after a day's use and the microbial content and endotoxin concentration determined.

Results The total viable count of bacteria before cleaning varied from 2300 - 8 x 10(4) cfu/ml and after from 0-40 cfu/ml. The endotoxin concentrations before cleaning varied from 360 - 2200 EU/ml and after 0-80 EU/ml.

Conclusions The reservoirs of non-vacuum benchtop autoclaves can become severely contaminated with micro-organisms particularly Gram-negative bacteria. The endotoxin content of the reservoirs can get to high and unacceptable concentrations. Draining the water reservoir and cleaning on a daily basis reduces the microbial content and the endotoxin concentration to acceptable levels.