The constantly occurring cases of environmental pollution of water by chemicals and pharmaceuticals and their degradation products show the importance of a close surveillance of potential bioactive substances in water. Common chemical sensors detect known substances with high sensitivity, but their bioactivity remains unknown. The innovative cell based sensor technology uses eukaryotic cells as the sensitive layer for an online cytotoxicity sensor. Therefore this technology may be used for evaluation of the cytotoxic and bioactive potential of water. To prove the usability of eukaryotic cells as sentinels for water pollution we show the cultivation, their vitality and metabolic activity of several cell types growing on the silicon surface of the metabolic chip (Micronas) using the Bionas 2500 analyzing system (Bionas). With the most feasible cell type a close to application trial was performed.