The location of big SWRO plants is usually limited by environmental restrictions such as the presence of the Posidonia habitat in the Mediterranean coast. The unknown impacts of brine on the flora and fauna associated at sea grasses has caused environmental damages either high cost disposal solutions of doubtful viability. Previous to the construction of 160.000 m(3)/day SWRO Plant in the southeast coast of Spain, an unique research study was carried out in the Mediterranean coast by some of the most advanced Spanish Research Centres in cooperation with two Spanish universities. The knowledge of the Posidonia limits can help not only to locate Desalination plants but to design disposal devices. This paper reports the results of two years study testing the salinity impact on Posidonia habitat lab and field with brine produced with a SWRO pilot plant. Additionally a brine disposal model has been developed to support the design of a full scale disposal system.