The remarkable development of reuse of water in Spain has taken place not only because of the necessity to extend water supplies, but also due to the requirements to improve the management in water treatment. Water supply consumption has increased, along with the increase of population that has taken place in numerous urban zones. As a result, traditional supplying sources are insufficient to satisfy the demand, which is in permanent expansion. This paper will analyze from an economical point of view, the effects of the Directive 91/271/EEC in Spain, as well as the new rule that appears in the Order in Council of December 8, 2007 in which the legal regime of treated water reuse is established. Furthermore, costs of reused and recycled water by means of different treatment systems will be discussed, as well as the environmental costs associated to them.