In ten videotaped socio-scientific debates related to water, students from Mexico, the USA and France tend to focus on few alternative positions. On the basis of Grize's definition of schematization, we followed their reasoning by studying how they put light on specific aspects of the discursive object 'water'. Through textometrical analysis of debate transcripts, we specified 6 characteristics of 'water' that are more or less emphasized depending on the prevailing national argumentative scenario.