Policy paper

Desalination for public water supply: Environment Agency position statement

Published 8 October 2025

Applies to England

1. Purpose

This statement sets out the Environment Agency’s position on desalination as an option for public water supply in England. We recognise the need for desalination as part of a diverse range of supply and demand options to secure resilient water supplies for the future.

This position statement is for the water industry, regulators and environmental groups interested in future water security and the development of strategic water supplies. It focuses on why this type of option should be considered by water companies and the Environment Agency’s role in respect of relevant planning and permitting requirements.

2. What desalination is

Desalination is the treatment of brackish (slightly salty water from river estuaries) or seawater to remove dissolved salts and other organic chemicals to provide a source of fresh water. After treatment, this can be suitable for drinking. There are 2 main methods of desalination: 

2.1 Membrane processes

Membrane processes primarily use reverse osmosis, where the water is forced through a membrane at high pressure. The dissolved salts and other organic chemicals in brackish or seawater cannot pass through the membrane, so stay on one side with treated water on the other. Electrodialysis is another, less commonly used, membrane process for desalination.

2.2 Thermal desalination (distillation)

Thermal desalination (distillation) involves heating saltwater so it evaporates, leaving behind the salt. The water vapour is then condensed to collect freshwater, which is treated to drinking water standards.

Most new desalination plants use the membrane process of reverse osmosis, which uses less energy than the more traditional thermal desalination processes. 

3. Why desalination is needed

The impacts of climate change, population growth, and the need to increase resilience to drought mean that we need to act now to ensure our water supplies are resilient. This is necessary to meet the needs of all users in the future.

Part of that action involves exploring new or alternative ways to increase water supplies, with desalination being one possible option. The national framework for water resources, published in June 2025, reported on pressures facing England’s water supply. It detailed the significant future supply deficit likely to occur without intervention.

This analysis is supported by studies including the National Infrastructure Commission’s preparing for a drier future (2018) and Water UK’s water resources long-term planning framework (2016). These studies all recommend increasing the future resilience of supplies through investment in both demand management and new supply options. 

4. Benefits of desalination

Desalination provides many benefits, including:

• providing very high security of supply, with seawater being effectively an unlimited resource
• supplying water in areas where demand is likely to exceed fresh water supply available from groundwater or rivers
• diversifying the water resources available and providing a resilient source particularly valuable during drought
• offering a steady, rainfall-independent source of water
• benefitting from continuing research and innovation, and technological advances that drive more energy-efficient and environmentally sustainable methods of producing potable water (drinking water that meets safety standards)

5. The Environment Agency’s position on desalination

The Environment Agency supports the development of resilient water supplies, including exploring various options to meet future demands. We believe that desalination could play an effective and increasing role in securing water supplies, enabling water companies to maximise available resources. We encourage desalination to be considered as part of a diverse range of supply and demand solutions.

Water companies may need to include desalination as an option in their water resource management plans (WRMP) to increase resilience. This is particularly relevant where other options are limited, and locations are suitable. We are aware that several desalination scheme proposals are being developed. Water companies must demonstrate in their WRMPs how they could secure water supplies sustainably using desalination schemes. We expect them to take into account demand management and other supply options.

We believe that desalination schemes should play a larger role in our future national water supplies, provided appropriate environmental protection and mitigation measures are in place. All schemes must secure permits, which will be conditioned to protect and enhance the environment.

6. The Environment Agency’s role

The Environment Agency has many roles in supporting and regulating desalination schemes, from strategic planning through to operational delivery. Our involvement spans the entire development process, ensuring schemes meet environmental standards while contributing to secure water supplies.

6.1 As a regulator and statutory consultee

The Environment Agency has several roles within the water resource planning process. Within our statutory duty to manage water resources and protect the environment, we aim to make sure there is enough water for society, the environment and the economy.

We are a statutory consultee in the water company WRMP process and review these plans. These set out how water companies will meet demand for the next 25 years or more. We ensure water companies follow the water resource planning guideline (WRPG), use relevant and appropriate methodologies and modelling to support these plans. We also review the non-statutory regional water resource plans produced by 5 regional water resource groups. 

We are also a statutory consultee of the planning process when a scheme applies for either a development consent order or local planning consent. As the regulator, we determine any environmental permit applications, including discharge and abstraction permits. These permits outline environmental requirements the schemes will need to meet and, where possible, provide environmental enhancement.

Once the desalination plant is operational, we ensure that the permits are complied with and will take enforcement action if they are not.

6.2 As part of our strategic water resource management responsibilities

We work closely with water companies through the development of a desalination scheme proposal to ensure that environmental assessments are appropriate. We also check that environmental impacts can be mitigated, and where possible additional benefits for people and the environment can be achieved as part of the scheme. 

Several proposals for desalination schemes are being progressed through the Regulators Alliance for Progressing Infrastructure Delivery (RAPID). This is made up of the Environment Agency, Ofwat and the Drinking Water Inspectorate. Through RAPID we have a role in overseeing the development of selected strategic water resource options, such as desalination.

6.3 As an advisor

We provide advice to government on the content of WRMPs before the Secretary of State directs water companies to publish their final WRMP.

7. Desalination schemes in England

7.1 Current operations 

Thames Water’s Thames Gateway desalination plant is the only existing public water supply scheme in mainland England. It was built in 2010 to help secure water supplies to London during long periods of low rainfall. It has capacity to produce around 150 million litres of water per day (ML/d), enough for nearly 1 million people. The scheme takes water from the tidal River Thames, storing it in a reservoir to minimise salinity. Water is first treated by conventional settlement and filtration before the salinity is removed by reverse osmosis. It is then blended with another source and put into supply. The plant has experienced operational challenges since 2018. It has only operated on a few occasions and well below its original design capacity of 150 ML/d.

The Isles of Scilly produce around 40% of their water supply needs from a desalination plant, which opened in 1992 and blends desalinated water with groundwater.

7.2 Future developments

Several desalination schemes are proposed in current water resource management plans WRMP24 and regional plans. The majority of these are located on the east and south coasts of England.

8. International experience with desalination

More than 150 countries use desalination for water supply. Notably, in the Middle East, Australia and North Africa, desalination has been integral to national water strategies for many years. Several countries such as Malta and the Maldives meet most of their water needs through desalination, while Saudi Arabia sources around 50% of its drinking water from this process. United Arab Emirates has some of the largest capacity desalination plants in the world.

Spain ranks among the top countries globally for both the number and capacity of desalination plants. With over 750 plants, including 99 large-scale facilities, Spain produces a substantial amount of desalinated water, primarily for urban areas and agriculture, particularly in regions like the Canary Islands and the Mediterranean coast, which are prone to drought.

9. Addressing concerns about desalination 

Desalination is now a feasible alternative supply option, with appropriate regulations, improved technology and reliable monitoring and control systems, and integration with renewable energy sources. Appropriate permitting from relevant regulators must be secured. This will likely involve Natural England and the Marine Management Organisation due to the coastal or estuarine nature of the resource. This is in addition to the Environment Agency, Drinking Water Inspectorate and local authority. Potential concerns can be addressed with appropriate planning, design and mitigation measures.

9.1 High energy costs

Energy considerations are being addressed through new and continuously developing membrane technology that is less energy intensive than more traditional thermal processes.

9.2 High financial costs

Costs associated with building and maintaining desalination plants require clear justification and will be accounted for in options appraisal process.

9.3 Reliance on fossil fuels

Water companies in England must consider the feasibility of desalination in line with their commitment to net zero by 2030. This requires a shift towards low-carbon energy sources to power desalination plants that can help reduce emissions.

9.4 Waste product concerns (brine discharge or chemicals)

Environmental impact assessments (EIA) will be required for all desalination proposals. This will be to assess impacts, define mitigation required and to gain all the necessary permits prior to implementation of a scheme. These must include consideration of brine concentration, the receiving environment, and assessment of mixing processes and dispersion at the proposed discharge locations.

9.5 Location

Sites selected must be suitable for desalination plants. There will need to be appropriate discharge points to ensure protection of sensitive marine environments, such as Maerl ‘carpets’ and seagrass meadows. Underwater infrastructure may need marine licences, with mitigation measures, such as eel screens considered dependant on impacts to habitats and species present.

9.6 Transporting water

This requires adequate consideration of costs and methods for moving desalinated water, potentially over considerable distances. Proposals should minimise impacts from transportation using existing infrastructure where possible for blending and distribution. 

9.7 Additional water requirements

Availability of water required for blending with the desalinated water will form part of feasibility assessments. This is required to prevent damage to the pipe network and to ensure it meets drinking water quality requirements.

9.8 Effective operation

Desalination plants may be designed for continuous use so they can be less efficient if they operate on a stop-start basis.

10. Contact the Environment Agency

General enquiries

National Customer Contact Centre
PO Box 544
Rotherham
S60 1BY

Email enquiries@environment-agency.gov.uk

Telephone 03708 506 506

Telephone from outside the UK (Monday to Friday, 8am to 6pm GMT) +44 (0) 114 282 5312

Monday to Friday, 8am to 6pm.