Engineering for scarcity:

Desalination, often associated with seawater, can also be applied to brackish and other saline sources. At its core, membrane-based desalination, using reverse osmosis (RO) and, sometimes, nanofiltration (NF) processes, removes salts, minerals, and in some cases, various organic compounds. This makes it a highly effective method for meeting increasingly stringent water quality standards. 

One of the advantages of RO is its ability to act as a reliable barrier to contaminants, particularly when compared to more conventional treatment methods. However, its success depends heavily on proper pretreatment and ongoing maintenance. Early desalination projects in the UK often struggled with this, resulting in fouled membranes and unexpected operation and maintenance (O&M) costs. 

Desalination and water reuse typically share some similar technologies, namely, membranes for removing contaminants. At present, in the UK, both desalination and water reuse markets are less mature than those in other parts of the world, such as the Middle East, Australia, North America and Singapore. 

Desalination is not used at a significant scale in Wales or Scotland. Water reuse in Wales is a longer-term ambition as part of a circular economy and aim to achieve carbon neutrality by 2040. The focus for water reuse in Scotland is improved management of rainwater sources. Arguably, the pressure to identify available and sustainable water sources is greatest in England, particularly in the southern part of the country. Several desalination and water reuse schemes are being proposed and, in some cases, developed by water companies in England, as described in their Water Resource Management Plans (WRMPs). 

Desalination and water reuse are best viewed as options within a broader water resource strategy. They are particularly relevant for scenarios where supply needs to be supplemented, such as in areas experiencing seasonal demand peaks or long-term water stress. Membrane-based technology, whether it be RO, NF, ultrafiltration (UF), or microfiltration (MF), will feature in a range of water and wastewater treatment applications as part of desalination or reuse schemes going forward.

While desalination and water reuse have valuable roles, scaling them up in the UK presents a complex mix of technical, economic, planning, regulatory, and environmental considerations.  

Desalination 

From a process standpoint, desalination involves pumping water at high pressure through membranes — a method that requires significant energy and generates a highly saline brine stream. 

Pretreatment is critical. If the pretreatment is insufficient, membranes are prone to fouling, leading to frequent and costly membrane replacements and operational inefficiencies. Careful pretreatment selection and advances in membrane technology, more efficient pumps, energy-recovery devices, and modular plant design are helping reduce these risks and costs. Machine learning algorithms are being increasingly used to further reduce O&M costs, and brine valorisation can sometimes be used if there is a viable market for minerals or metals extracted from brine. 

Water reuse 

In the UK, there are currently no direct potable schemes (treatment plants that treat wastewater to drinking water quality and introduce the water directly into the distribution network) under development. Several indirect potable schemes are being developed, where wastewater is treated, typically to or near drinking water quality and returned as a water source. This is achieved by blending the reused/recycled wastewater in a reservoir, river or aquifer, as part of the water resource catchment, to be further treated by a water treatment plant and pumped into the drinking water supply network. 

Desalination and water reuse are being developed in targeted ways to supplement supply during periods of heightened demand. Their broader adoption depends on technical feasibility and careful consideration of economic, environmental, and regulatory factors. Whilst desalination and water reuse can be effective options in water-stressed contexts, national policy continues to prioritise efficiency and demand management as foundational measures. 

Graham Bateman notes, “It’s not about shoehorning desalination or water reuse into every possible scenario but about having the knowledge to know where, when and why — they work as viable solutions. Desalination or water reuse schemes will increasingly feature as part of an integrated approach to water management.” 

Planning with people, not just systems 

Implementing desalination or water reuse projects requires long-term thinking, cross-sector collaboration, careful environmental planning, and strong technical and engineering capabilities. 

Projects benefit from early stakeholder engagement to assess technical feasibility and anticipate how future regulations, costs, and environmental performance may shift over time. For desalination, this is particularly important in managing brine discharge and protecting marine ecosystems. Effective intake design, brine dispersion modelling, and the use of subsea filtration techniques are just some of the ways these impacts can be reduced. 

Energy consumption remains a challenge. Historically, desalination relied on fossil fuels, but a growing number of projects are now using renewable sources or low-carbon energy mixes. This shift is already visible in regions like the Middle East, where membrane-based systems are replacing thermal plants for their relative efficiency. For water reuse, significant developments in technology, science, policy, education, planning and economic feasibility are underway. 

GHD treats desalination and water reuse as part of a wider offering, deployed when they meet the long-term needs of clients and communities. With sound planning, transparency, and context-driven application, desalination and water reuse will contribute meaningfully to water security. 

Takeaways for planning a resilient water supply 

• Desalination and water reuse/recycling have a place in the UK’s long-term water strategy but must be considered carefully alongside other supply and demand options. 

• Pretreatment and maintenance planning are crucial for plant performance and longevity. 

• New technologies and configurations are lowering energy use and increasing recovery rates. 

• Environmental impacts must be addressed at every stage, from intake design to brine discharge and pumping to the point of use. 

• Stakeholder engagement and policy context are integral to successful implementation.