A reduction-aeration method is optimized for the analysis of mercury at the ng.I−1-level in drinking-water. The parameters investigated are: the aeration time, the flow rate of the aeration-gas, the type of gas distributor, the amount of reductant and the mercury concentration. To improve the sensitivity, the mercury aerated is preconcentrated on a gold-coated quartz-sand absorber which is analysed by thermal desorption and CVAAS. In this way, the interference by water vapour is avoided and the calibration is simplified.