The analysis of water samples using gamma spectrometry requires the preconcentration of the sample in order to determine the content of low-level radionuclides. An automated evaporator was used for this purpose during the preparation of approximately 250 samples per year as part of the monitoring programmes performed in Slovenia. Since an automated sample-evaporation procedure has not yet been reported in the relevant literature, our unique, innovative, in-house-constructed system is described in terms of developing the design, its optimization and automation.