The excessive focus on water mounts a challenge to the sustainable development. Energy is another aspect that should be taken into account. Nexus approach is characterized by an equal emphasis on energy and water spheres. In arid areas, like the city of Kashan, Iran, non-conventional waters (e.g. desalinated and recycled waters) have been considered as an alternative resource of water. Nexus warns that alternative resources should be tapped in with consideration of the costs and environmental impacts of the energy. In this study, the allocation of demands and supplies in the basin are primarily modeled by WEAP. Then, the energy required to generate water is simulated by LEAP. Finally, using the optimization method, the desirable volume of non-conventional water is estimated. The results suggest that the maximum capacity of the non-conventional water is not necessarily the optimal point. Thus, despite high potentials for producing non-conventional water, caution should be practiced in setting proper limit for the production.