Seawater desalination

Three main factors explain the growing demand for seawater desalination over the past 15 years:

• demographic development and its amplifier: the migration of rural populations to cities, and mainly to the largest cities;

• the fact that more than a third of the world's population and more than half of all megacities (cities with more than 5 million inhabitants) are concentrated in a coastal strip 150 km deep, where there is rapidly growing demand from all sectors of human activity: domestic, industrial, tourist and agricultural water, etc. At the same time, the rivers that feed it are becoming increasingly polluted, and have already been subjected to ever-increasing withdrawals (mainly for agricultural irrigation);

• In addition, technical advances in the two technologies used in seawater desalination have resulted in lower investment costs (increasing size of units built, improved membranes used in reverse osmosis (cf. permeability and salt passage)...) and, above all, reduced operating costs, particularly for the reverse osmosis process whose specific energy demand (kWh/m ³ of water produced) has fallen by 40% in 15 years... All of which makes for a more attractive offer.

Strong demand and more attractive supply explain the market's overall growth of more than 10% per year and its globalization: 15 years ago, the market was still highly concentrated in the Middle East (Saudi Arabia, United Arab Emirates [UAE]), but it now extends to the entire Mediterranean rim (Spain and Algeria in particular), the Caribbean, the southern United States, Australia, and recently China, India...

A 2008 study counted 13,800 plants in operation, of which 60% were reverse osmosis plants and 40% distillation plants, but as the capacity of the latter is higher, their respective contributions are reversed.