Water policies have been implemented worldwide to face water stress. However, the existence of water users' groups with opposite interests and different political power results in the plain failure or low effectiveness of water policy reforms. A better understanding of users' perceptions regarding policy outcomes is important to avoid the failure of water policies and the intensification of water conflicts. This paper empirically examines the divergent perception of interest groups on the implementation of different policies dealing with water scarcity and their proactive involvement with water agencies. We have conducted a survey in the Jucar River Basin (a water-stressed basin in southeastern Spain) to analyze interest group opinions regarding water policy effectiveness and water institutions' performance in water management. Questionnaires were sent to the main irrigation districts and urban water utilities within the basin. The collected information gives a general picture of the behavior of opposite water interest groups in this basin. The analysis of the perceptions on water policy reform between the groups highlights the existence of significant differences between preferred measures to address water scarcity and lobbying capacity. These differences depend on the size of the group, the specific basin location, and other group characteristics.