In Sardinia, as in many other Mediterranean regions, recurrent droughts and climate change have dramatically reduced available water resources. As a result of this critical situation, in 1995 the Italian Government declared a state of emergency and drew up a program for financial support by the State and local authorities with the aim of reducing this serious deficit. One of the actions focused on reclaiming and reusing the effluent from the sewage treatment plant of Cagliari. This article reports on the multidisciplinary preliminary study performed by the Ente Acque della Sardegna (ENAS) to evaluate the suitability of reusing Is Arenas effluent for irrigation and on the operation of the tertiary treatment plant.