As water scarcity intensifies around the world, desalination is becoming an increasingly important source of freshwater. Reverse osmosis is the most mature and widely established desalination technology, playing a key role in providing reliable water supplies across many regions.
Building on the same proven process, deep-sea desalination proposes relocating part of the process to the ocean floor, where natural hydrostatic pressure may contribute to system operation.
This article covers the following topics:
As climate change intensifies and populations grow, pressure on freshwater resources is reaching unprecedented levels. Between factors like prolonged droughts and overexploited aquifers, water scarcity is no longer just a regional concern, it’s becoming a global challenge. A study released in early 2026 even stated that we’re entering an era of global water bankruptcy.
Desalination is an increasingly important solution, transforming seawater into drinking water for millions of people. A new approach reimagines where and how this technology works: deep-sea, or subsea, desalination. By moving desalination systems from the shoreline to the ocean floor, this method explores the use of the deep ocean's natural hydrostatic pressure to support the reverse-osmosis process. While still in its early stages, deep-sea desalination is attracting growing interest as a potential complement to existing water supply strategies in specific contexts.
Deep-sea desalination uses the same fundamental process as conventional desalination plants: reverse osmosis. Seawater is pressurized and forced through semi-permeable membranes that filter out the salt and impurities, only letting water molecules pass through.
In deep-sea systems, however, that same pressure is provided naturally by the ocean. At depths of several hundred meters, hydrostatic pressure can reach levels sufficient to drive reverse osmosis with far less mechanical input. Subsea desalination systems—often designed as modular units placed on the seabed— seek to take advantage of these conditions as part of the desalination process. Seawater enters the system at depth, passes through membranes under natural pressure, and the resulting fresh water is then pumped up to shore via pipelines. This still requires energy, as does operating auxiliary systems, but subtracting the pressurization component may contribute to the reverse-osmosis process, although the overall benefits depend on site-specific conditions.
“Beyond the specific technology involved, the main challenges facing large-scale desalination remain linked to energy consumption, environmental sustainability, and, to a lesser extent, long-term operational reliability. Energy continues to be the largest component of operating costs, making access to a stable, competitive, and low-carbon energy supply essential,” notes Mireia Marcé, Innovation Engineer at ACCIONA.
Surface seawater conditions can vary over time depending on local environmental factors. In deeper waters, however, water quality tends to be more stable, with lower levels of organic matter and suspended solids. One of deep-sea desalination’s main advantages is the ability to draw water from greater depths, where water quality is typically more stable and organic matter content is lower.
Because subsea systems are so far below the ocean’s surface, they’re protected from storms, waves, and other extreme weather events. This can enhance resilience, particularly in regions prone to hurricanes or coastal flooding. Finally, subsea systems are often designed as modular units that can be deployed incrementally. This allows for flexible investment and capacity expansion, aligning supply more closely with demand.
One of deep-sea desalination’s main advantages is the ability to draw water from greater depths, where water quality is more stable and organic matter content is lower. "
“One of deep-sea desalination’s main advantages is the ability to draw water from greater depths, where water quality is more stable and organic matter content is lower. This can simplify pretreatment systems and potentially reduce both capital and operating expenditures at this stage of the process. Additional benefits include a reduced visual impact and more efficient dilution of the brine discharge,” says Sandra Martínez, Innovation Engineer at ACCIONA.
Although deep-sea desalination is still an emerging technology, several companies and research initiatives are working to validate different technological approaches and assess their technical and economic viability under real operating conditions. For example, a California-based startup is progressing through pilot validation of its “deep-sea water farm” concept, which also uses modular subsea pods Meanwhile, other startups have focused on prototype development and concept validation, often targeting specific applications or niche and mobile use cases as a pathway to market entry.
For established leaders in desalination such us ACCIONA these developments represent both an opportunity and a point of integration. “The global water system is likely to evolve toward a more diversified technological landscape, where success will depend not on a single dominant solution, but on the effective combination of technologies adapted to the needs of different environments,” says Martínez.
As offshore wind and other marine-based energy systems expand, there’s also growing interest in integrating water production with energy generation.
As offshore wind and other marine-based energy systems expand, there’s also growing interest in integrating water production with energy generation. Subsea desalination could potentially play a role in these hybrid systems, creating new synergies between sectors and contributing to a more integrated approach to marine infrastructure.
Despite its promise, deep-sea desalination also faces significant challenges that must be addressed before it can be deployed at scale. As with many emerging technologies, initial costs are high. Subsea systems require specialized engineering, materials, and installation techniques. Demonstrating cost competitiveness with established desalination methods will be critical.
Similarly, operating equipment on the seabed introduces logistical complexities. Maintenance and repair require specialized vessels and expertise, and long-term reliability must be proven under harsh conditions, including high pressure and corrosive environments. Though hydrostatic pressure can contribute to part of the pressure requirements of the reverse osmosis process, energy is still required to make the system work. A significant share of the energy demand is associated with transporting the produced water to shore, while additional power is required to operate auxiliary systems.
The environmental impact of subsea desalination is still being studied. While offshore placement may reduce some coastal impacts, questions remain about how intake and brine discharge could affect deep-sea ecosystems. And lastly, not all coastlines are suitable for subsea desalination. The approach is most viable in regions where deep water is accessible relatively close to shore, limiting its applicability in some parts of the world.
As the global water sector evolves, it’s becoming increasingly clear that no single solution will be sufficient to address the complexity of water scarcity. Instead, a portfolio of technologies—tailored to local conditions and needs—will be required.
In this context, deep-sea desalination represents an interesting addition to the water technology toolkit. It introduces a different approach to how and where desalination can be deployed, particularly in regions where access to high-quality seawater at depth may offer advantages in terms of pre-treatment requirements and operational design. However, it’s not yet mature technology, and its ultimate role in the global water landscape has yet to be fully defined. Deep-sea desalination opens up new possibilities, although its benefits will ultimately depend on the specific conditions of each site.
The coming decade will be critical in determining whether subsea desalination can scale to meet real-world demand.
As innovation continues and pilot projects transition into commercial operations, the coming decade will be critical in determining whether subsea desalination can scale to meet real-world demand. At the same time, large-scale, land-based desalination plants will continue to play a central role in supplying reliable, high-volume water to cities and industries around the world.
For companies like ACCIONA, with deep expertise in desalination and a strong commitment to sustainability, the challenge—and the opportunity—lie in exploring how these emerging approaches can complement existing solutions and contribute to a more resilient and diversified water mix.
“The combined pressures of population growth, urbanization, rising industrial and agricultural demand, and especially the cumulative effects of climate change have significantly reduced the resilience margins of many water systems. The challenge is no longer simply one of managing droughts, but of redefining the mix of available water sources and ensuring water supply and resilience under increasingly extreme conditions,” says Marcé.
Sources:
Vanessa Bates Ramirez is a science and technology journalist specializing in energy, climate tech, and artificial intelligence. Her work has appeared in New Scientist, Scientific American, IEEE Spectrum, Singularity Hub, and other outlets.