Today ecotoxicological evaluations of surface water quality are either based on field surveys or online biomonitoring, whereas the ecotoxicological quality of wastewater is mostly determined with standardised acute toxicity tests. In this paper we present a concept for the ecotoxicological evaluation of surface waters, where mainly in vitro tests are used for the screening of water samples, presenting the first tier of a two-tiered approach. In this first tier a battery of fast and cost-efficient test systems are used as an early warning system. Thereby, the toxic potential of water samples will be identified. This modular approach allows the exchange or addition of test systems if necessary. If a toxic potential is identified in a water sample, this sample can be investigated more thoroughly in a second tier where organisms are used. In this paper we focus mainly on the general approach and the description of the first tier
