Desalination

Desalination is a set of physico-chemical processes that remove salts and other dissolved minerals from seawater or brackish water to produce freshwater. It has become an important source of supply in arid and coastal regions facing water stress, complementing conventional sources and reuse.

According to the International Desalination and Reuse Association (IDRA), global installed desalination capacity is on the order of 90 to 115 million cubic metres per day (depending on whether commissioned or contracted capacity is counted), and it continues to grow.

Main technologies

• Reverse osmosis (RO): the dominant technology, accounting for roughly 70% of global capacity. It pushes water through semi-permeable membranes under pressure. Whole-plant energy use is typically around 3 to 4 kWh per cubic metre for seawater, lower than thermal processes.
• Thermal processes (MSF and MED): multi-stage flash and multi-effect distillation, which evaporate and condense water. They are more energy-intensive (commonly in the range of 10 to 20 kWh per cubic metre or more) and remain common in the Middle East, where thermal energy is abundant.
• Emerging approaches: improved membranes, energy-recovery devices, and coupling desalination with renewable energy to cut costs and emissions.

Benefits

• Provides a supply that is largely independent of rainfall, improving resilience in water-scarce areas. In Spain, the Canary Islands and parts of the south-east depend heavily on desalination.
• Reduces extraction from coastal aquifers, helping to limit saltwater intrusion.
• When powered by renewable energy, it substantially lowers the associated carbon footprint.

Environmental challenges

• Energy consumption: desalination is energy-intensive, so the emissions depend strongly on the electricity mix; renewable power is key to reducing them.
• Brine: the concentrated, hypersaline by-product must be managed carefully (diffusers, dilution, or further treatment) to limit impacts on marine ecosystems near the outfall.
• Marine intake: water intakes can harm marine life, which is mitigated with low intake velocities, screening, and subsurface intakes.

Costs and outlook

The cost of desalinated water has fallen over recent decades thanks to more efficient membranes and energy-recovery systems, although it remains sensitive to energy prices. Spain is one of the leading countries in desalination in Europe, with significant installed capacity serving both urban supply and irrigation.

Desalination in context

Desalination is most sustainable when it is integrated with renewable energy, paired with responsible brine management, and combined with demand-side measures such as efficiency and water reuse within a wider water security strategy. Treated as one option among several, it can strengthen supply resilience while keeping environmental impacts in check.

At Manglai we help companies measure their carbon footprint and prepare their sustainability reporting, including the impact of energy-intensive processes such as desalination. Discover how Manglai can help you.