This paper proposes a simple method for decomposing the temporal changes in water intensity into different driving factors. Specifically, total changes are split into three elements that clarify some of the hidden reasons behind the changes in water use over time. The first element captures the changes in water intensity due to sectoral uses, showing the effects of modifying the water intensity of the different production sectors; the second element shows the changes in sectoral output intensity, showing the influence on water consumption of altering the production structure; finally, the third element quantifies the effects of the changes in residential water intensity, showing the contribution that changing the final water uses makes to changing water intensity. The empirical application, which is for the Spanish region of Catalonia, uses the latest available water consumption data (for 2004 and 2007). The results show a reduction in the regional water intensity resulting from a reduction in the water intensity of agriculture and industrial activities, which was greater than the increase in the water intensity by the services sectors. In addition, the production structure made a mixed contribution to final water intensity, depending on the sector under consideration. In particular, the decrease in the importance of agricultural production had the highest influence on reducing regional water intensity. Finally, the residential uses of water made a negative contribution to the total water intensity. The different directions and magnitudes of the drivers identified in this paper highlight the importance of using detailed and precise methods for studying water issues. Keywords: Sectoral Water Intensity, Sectoral Output Intensity, Residential Water Intensity, Mediterranean Region.