The growing demand for hydrogen as a clean energy carrier has intensified scrutiny over its production methods, particularly regarding resource use. Freshwater consumption for electrolysis and other hydrogen generation processes poses sustainability challenges, especially in water-scarce regions. An alternative approach involves leveraging saline or brackish water sources, which account for over 97% of global water reserves. This strategy could mitigate competition with agriculture and municipal needs while unlocking new opportunities for coastal and arid regions.

Desalination as a Precursor to Hydrogen Production
Most conventional hydrogen production methods, including electrolysis and thermochemical cycles, require high-purity water. Desalination of seawater or brackish water is a proven but energy-intensive solution. Reverse osmosis (RO) dominates modern desalination, with energy consumption ranging between 3–10 kWh per cubic meter of water, depending on salinity levels and system efficiency. Multi-stage flash distillation and electrodialysis are alternatives, though they typically exhibit higher energy penalties.

Integrating desalination with hydrogen production introduces a compounded energy burden. For example, producing 1 kg of hydrogen via electrolysis requires approximately 9–10 liters of pure water. When accounting for desalination, the total energy input increases by 5–15%, varying with feedwater salinity and technology choice. Hybrid systems, such as solar- or wind-powered desalination coupled with electrolyzers, can offset these penalties by using renewable energy that would otherwise be curtailed.

Direct Saline Water Electrolysis: Innovations and Challenges
Recent research has focused on bypassing desalination entirely by adapting electrolyzers to operate directly with saline or brackish water. Traditional proton-exchange membrane (PEM) and alkaline electrolyzers suffer from chloride-induced corrosion and catalyst poisoning when exposed to untreated seawater. However, advances in anode materials, such as titanium substrates coated with iridium oxide, have demonstrated improved resistance to chloride attack.

Another promising development is the use of asymmetric membranes that selectively block chloride ions while permitting proton transport. Experimental systems have achieved Faradaic efficiencies exceeding 90% in laboratory settings, though durability beyond 1,000 hours remains a hurdle. Osmotic energy recovery systems, which harness salinity gradients to partially offset electrolysis power needs, are also under investigation.

Environmental Trade-Offs and Regional Considerations
While saline water use alleviates freshwater stress, it introduces other environmental concerns. Desalination brine, often discharged back into marine ecosystems, can elevate local salinity and harm benthic organisms. Direct electrolysis avoids brine production but may release trace chlorine gas as a byproduct, necessitating gas-scrubbing systems. Coastal regions with abundant wind or solar resources are ideal candidates for these systems, as renewable energy can mitigate both carbon emissions and operational costs.

The Middle East and North Africa (MENA) region exemplifies this potential. With high solar irradiance and limited freshwater, countries like Saudi Arabia and the UAE are piloting solar-driven seawater electrolysis projects. Similarly, offshore wind farms in Northern Europe could couple with marine-based hydrogen production, reducing land-use conflicts.

Economic and Scalability Factors
The levelized cost of hydrogen (LCOH) from saline water depends heavily on energy inputs and infrastructure proximity. Desalination adds $0.10–$0.30 per kg of hydrogen, while direct electrolysis systems currently incur a 20–30% premium over freshwater systems due to material costs. However, economies of scale and material innovations could narrow this gap. Pilot plants in Australia and the Netherlands aim to validate commercial viability by 2030.

Regulatory frameworks must also evolve to address water sourcing and discharge permits for large-scale projects. Coordination between energy and water policymakers will be critical to ensure sustainable deployment.

Conclusion
Utilizing saline or brackish water for hydrogen production presents a feasible pathway to reduce freshwater dependency, particularly in coastal and arid zones. While desalination-integrated systems offer near-term solutions, direct electrolysis technologies hold long-term promise if durability and cost challenges are overcome. Environmental impacts require careful management through brine minimization and renewable energy integration. As the hydrogen economy expands, regional adaptations of these technologies will play a pivotal role in achieving both energy and water sustainability goals.