Water desalination processes have contributed to a better standard of living in a number of countries during the second half of the 20th century, following an increase in water demand for drinking purposes as well as industrial and agricultural uses. However, the technologies used in water desalination are also accompanied by adverse environmental effects. There are several effects to be considered in desalination plants, such as the use of the land, the groundwater, the marine environment, noise pollution and the use of energy, amongst others. To protect and preserve the environment, most countries turned to assess the environment impacts produced by desalination plants. Seawater desalination plants are located by the shoreline, to supply desalted water to the population of the main cities and other uses. The construction of both the desalination plants and all the required infrastructure in coastal areas affects the local environment. The impact on groundwater is due to the seawater pipes leaks which could contaminate the aquifers. The high salt concentration in the brine and several chemical products used in the desalination process are returned to the sea. Most impacts on the marine environment arise as a consequence of the brine discharge and their effects could be worse in the Mediterranean sea than in other areas. With respect to the noise pollution produced by the desalination. plants, there is always an impact on the plant operators and also on the towns and villages nearby. One of the major indirect environmental impacts is the use of the energy required by desalination plants, particularly when electricity is produced by burning of oil, which in turn boosts the process of global warming. In this paper, we analyse the environmental problems of seawater reverse osmosis desalination plants, focusing on some case studies located in Canary Islands, and describing the major impacts identified. Environmental monitoring is done by the water and environmental authorities, based on regional regulations which turn out to be more restrictive than national legislation.