The significant unbalance between water resources and the huge demands in Mediterranean area in Spain (especially for irrigation and tourist infrastructures) entails the necessity of a careful water management. The Spanish Water Resources National Plan (PHN, 2005) foresees to achieve 3 Mm(3)/day of water resource through a significant increase in the desalinated water production, water recycling and modernization of irrigation and supply infrastructures. With respect to desalination, this plan foresees an additional flow rate of 1.55 Mm(3)/day. The plants projected under the PHN (2005) use reverse osmosis technology with conversion rates between 40% and 50%, with the amount of fresh desalinated water and brine effluent being similar. The brine is discharged into the Mediterranean coastal waters, causing a potentially harmful impact on the marine environment, especially on the stenohaline benthic communities: Posidonia oceanica and Cymodocea nodosa seagrasses. In this paper, the evolution and growth of desalination in Spain is summarised. Brine behaviour, environmental evaluation methodologies, marine monitoring programs and action protocols set up to guarantee the protection of the marine environment are described. A few examples of recently built desalination plants are explained. Based on this experience, some recommendations to improve the discharge system designs are given to minimize impacts. (C) 2010 Elsevier B.V. All rights reserved.