A disposable all-solid-state planar-type potentiometric electronic tongue has been developed with a five-sensor array screen-printed on a polymeric substrate. The fabrication method enables simple and reproducible mass-production of low-cost electronic tongue systems, since the sensors showed good reproducibility (0.96% RSD), repeatability (0.58% RSD) and lifetime (8% decrease of sensitivity after 37 days in solution). The system was used for the simultaneous determination of NH₄ ⁺, K⁺ and Na⁺ ions in synthetic and natural surface water samples. The signals were processed by using a multilayer artificial neural network which was optimized for that purpose. Correct results were obtained for the three ions in synthetic samples. In natural surface waters, ammonium and potassium ions could be determined, while sodium ions showed biased results due to the effect of the complex matrix.