In Southern Europe numerous areas suffer water scarcity. For public policies to be effective, a thorough study of water users must be conducted. This paper aims to analyse the key factors that influence the decision of industrial users in urban areas when choosing between withdrawing water from underground sources or using water supplied through the public network. Using a database of industrial firms in Zaragoza (Spain) the proportion of water drawn from wells is considered as the dependent variable of a fractional response model. This methodology provides an original contribution to the field of behavioural analysis of the industrial sector, enabling us to model industrial decisions on water sources. The results obtained show that the most significant decision-drivers are how the industries use the water, the firms' location and the accessibility of the different sources. Moreover, the findings indicate that firms use lower proportions of well water during the summer.