The desalination sector has made major progress in reducing the energy required to produce fresh water. Reverse osmosis (RO) has become the dominant large-scale approach partly because it typically has lower specific energy consumption than thermal desalination processes, while advances in membrane design, pumps and energy-recovery devices continue to improve performance.
Energy consumption is therefore an essential measure of sustainability, but it should not be the only one.
A plant can achieve a competitive energy figure under ideal conditions and still carry a substantial environmental and operational burden through membrane fouling, chemical dosing, frequent cleaning, declining permeate output or recovery, component replacement and unplanned downtime. A more complete assessment should consider how reliably the plant sustains its performance throughout its operating life.
Fouling is an efficiency problem
Membrane fouling is often treated primarily as a maintenance issue. In reality, it affects almost every important performance measure within an RO system.
As scale, organic material, suspended particles or biological growth accumulate, hydraulic resistance increases. Operators may need to raise pressure to maintain output, while permeate flow and salt rejection can deteriorate. What begins as a surface-deposition problem can therefore become an energy, water-quality and asset-life problem.
This distinction matters because headline energy figures are generally most favourable when membranes are clean. The more meaningful question is how rapidly performance declines between cleaning cycles and how much intervention is required to restore it. A sustainable plant should not simply operate efficiently on commissioning. It should remain efficient and stable for as long as practicable.
The wider footprint of chemical use
Chemicals remain an important part of many desalination and RO pretreatment strategies. Antiscalants, biocides, coagulants, pH-adjustment chemicals and clean-in-place solutions can all perform necessary functions when selected and managed correctly.
However, their wider footprint should be recognised. Chemicals must be manufactured, transported, stored, handled and dosed. Cleaning also consumes water, creates waste streams and takes membrane trains out of productive operation. Excessive, incompatible or poorly controlled chemical cleaning can contribute to membrane degradation, increasing the likelihood of premature replacement. The objective should not be the unrealistic elimination of every chemical in every application. It should be to reduce avoidable dependency and use each intervention more precisely.
Where upstream treatment, improved monitoring or alternative conditioning methods can extend the period between cleans, reduce dosing requirements or preserve membrane condition, the sustainability benefit extends beyond the chemical saved. It may also include reduced downtime, lower waste generation, improved safety and longer asset life.
Recovery is about more than output
Water recovery is another area where a single headline figure can conceal operational trade-offs.
Increasing recovery can reduce the volume of feedwater required for each unit of permeate, but it also increases the concentration factor within the membrane array and in the concentrate stream. This can increase scaling risk and place greater pressure on pretreatment, membranes and cleaning regimes.
The most sustainable recovery rate is therefore not necessarily the highest technically achievable rate. It is the level that can be maintained without creating disproportionate energy use, chemical demand, fouling or loss of reliability.
Operators should assess recovery alongside normalised permeate flow, differential pressure, salt passage, cleaning frequency and the stability of these measures over time. This provides a more realistic view of whether an apparent improvement is genuinely sustainable.
Operational resilience must be counted
Desalination plants frequently support communities, industrial processes and facilities where water continuity is critical. Reliability is therefore an environmental and social consideration as well as a commercial one.
A process that depends on frequent intervention, specialist attendance or narrowly controlled operating conditions may perform well in a trial but be difficult to sustain at full scale. Conversely, a modest efficiency improvement that also reduces maintenance and stabilises water quality may deliver greater whole-life value.
This is particularly important as desalination expands into more varied settings, including smaller municipal plants, industrial reuse, mobile systems and inland brackish-water applications. Solutions must be judged not only by peak performance, but also by simplicity, maintainability and tolerance of changing feedwater conditions.
Learning from emerging evidence
Our own work at Sidon Water has reinforced the importance of measuring several outcomes together.
Independent bench-scale testing at Cranfield University evaluated upstream electrochemical water conditioning using synthetic freshwater, brackish-water and seawater matrices. Relative to untreated controls, permeability improved by approximately 9%, 12% and 8% respectively, while flux decline was reduced by approximately 32%, 41% and 30%. In the brackish-water matrix, lower passage of chloride, sulphate and calcium was also observed.
A subsequent short live SWRO campaign at the Instituto Tecnológico de Canarias recorded reductions of approximately 18.5–18.8% in normalised permeate conductivity and 1.2–3.1% in specific energy consumption across two treatment configurations, compared with baseline. These are encouraging early results, but longer-duration trials under more challenging feedwater conditions are required to quantify long-term effects on fouling, cleaning frequency and membrane life.
This is not an argument that one technology or pretreatment method will suit every plant. Feedwater chemistry, membrane configuration, recovery target and operating context remain decisive. It is an argument for wider and more disciplined measurement.
A broader definition of progress
The next stage of sustainable desalination will not be achieved through energy reduction alone. It will depend on plants that resist fouling, use chemicals more selectively, preserve membranes for longer, maintain water quality and continue operating efficiently as conditions change.
For operators and technology providers, this requires whole-life thinking. Trials should run for long enough to capture deterioration and cleaning behaviour. Performance claims should be normalised against feedwater, temperature and operating pressure. Chemical, maintenance and disposal impacts should be included alongside electricity consumption.
Energy will remain one of the sector’s most important metrics. But the most sustainable cubic metre of desalinated water is not simply the one produced with the fewest kilowatt-hours. It is the one produced reliably, with the least cumulative demand on chemicals, materials, labour, water and infrastructure.
Source note: Performance figures cited are drawn from independent bench-scale testing undertaken by Cranfield University and a 2026 live SWRO trial campaign at the Instituto Tecnológico de Canarias.
