For most buildings considered to be of a public non-residential type there are insufficient published data to establish and compare the theoretical standards with actual consumption data. Therefore, water consumption per user in non-residential buildings is still a very complicated issue for engineers and designers involved in analysing water demand and water management. This is why linking water consumption and school occupancy is the goal of this paper, trying to set the basis for further design, conservation and educational interventions on this topic. This research integrates quantitative data of water consumption, through water metering and analysis, and historical data about users in buildings. We focused on consumptions for four types of schools: nurseries (0–3-year-old children), kindergartens (3–6 years), elementary schools (6–11 years) and secondary 1st grade schools (11–14 years). The results are that the rational basic demand for water is estimated as 48.8 l per pre-school student per day and 18.7 l per elementary/secondary school student per day. Therefore we found that younger children use more water on a daily basis than older ones, probably because they need more services, such as laundries and kitchens, whereas older students consume water mainly in restrooms.