Since the first large-scale seawater desalination plants were commissioned in the early 20th century, tens of thousands of desalination facilities have been built worldwide. Desalination has become one of the key technological pathways for alleviating water scarcity in coastal and arid regions and for diversifying water supply sources.
Over the past several decades, technological progress in the industry has primarily focused on improving membrane performance, optimizing energy recovery systems, and managing concentrate discharge. Nevertheless, conventional large-scale land-based desalination plants continue to face persistent challenges, including high land requirements, significant energy consumption, and environmental pressure on nearshore ecosystems caused by high-salinity brine discharge.
In recent years, a new approach has emerged: relocating seawater desalination systems from land to the deep sea. By deploying modular reverse osmosis (RO) desalination units on the seabed, these concepts aim to harness the natural hydrostatic pressure of deep seawater to reduce the additional pressure required for RO operation. This approach seeks to achieve a new balance between energy efficiency, land use, and environmental impact.
From Land-Based Plants to Subsea Modules
Traditional desalination plants are typically constructed near coastlines and require extensive intake systems, pretreatment facilities, and large civil structures. In addition to occupying valuable coastal land, they rely on long intake and discharge pipelines and supporting infrastructure.
Next-generation “subsea desalination” concepts, by contrast, are built around subsea chambers or deep-sea modules. Core RO systems are enclosed within pressure-resistant structures and deployed on the seabed at depths of several hundred meters. The produced freshwater is then conveyed to shore or to industrial users via subsea pipelines.
This configuration is driven by two key considerations. First, deep-water hydrostatic pressure can be utilized to reduce the energy demand of high-pressure pumps, improving overall system efficiency. Second, relocating major infrastructure offshore significantly reduces coastal land use while discharging high-salinity concentrate away from sensitive nearshore ecosystems, thereby alleviating localized environmental stress.
Technical Pathways for Modular Deep-Sea Reverse Osmosis
Current explorations by teams in Northern Europe and North America largely follow a shared concept of “modularity combined with deep-water deployment,” although engineering implementations vary.
One Northern European desalination technology developer is working on a subsea desalination system composed of multiple deep-sea chambers forming an integrated “underwater water plant.” According to publicly available information, the system could reduce energy consumption by up to approximately 50% under typical operating conditions, while decreasing coastal land use by around 95%.
A U.S.-based marine technology company has proposed the concept of an “underwater water farm,” in which multiple subsea modules are arranged in a farm-like configuration. Public disclosures indicate that each module is designed for a capacity of up to one million gallons per day (approximately 3,785 m³/day). Through reverse osmosis, the system removes salts, bacteria, viruses, and certain organic micropollutants—including some pesticides and PFAS—with the goal of producing high-quality freshwater.
Another Northern European company has focused on applications in the Middle East and mining sectors, deploying modular deep-sea desalination units at depths of around 400 meters. Individual modules are designed for capacities of approximately 50,000 m³/day, and the company has announced cooperation with local phosphate mining operations to supply industrial water.
Across these concepts, modularity is a defining feature. Each subsea chamber is treated as a standardized, replicable production unit that can be scaled incrementally according to demand and optimized for varying water depths, temperatures, and salinity conditions.
Compared with conventional large land-based plants, this “on-demand scaling” approach allows for phased investment and facilitates water supply deployment closer to specific industrial clusters or remote coastal communities.
Energy Consumption and Environmental Impact: Insights from Early Pilots
A central value proposition of deep-sea desalination lies in reducing specific energy consumption by leveraging hydrostatic pressure to ease the load on high-pressure pumping systems.
In an early pilot project conducted by a Northern European company in Norway’s Boknafjord, publicly reported data indicate that, under specific operating conditions, the deep-sea system achieved approximately a 40% reduction in energy consumption compared with conventional land-based seawater RO plants. This result highlights the potential energy-saving advantages of this technological pathway.
From an environmental perspective, deep-sea deployment strategies typically emphasize three aspects. High-salinity concentrate is discharged at depths of several hundred meters, where larger water volumes and dynamic flow conditions enable faster dilution and dispersion, reducing localized salinity stress on nearshore ecosystems. Subsea installations also reduce or eliminate the need for large coastal facilities and intake–outfall structures, thereby minimizing impacts on coastal landscapes and terrestrial ecosystems. In addition, by optimizing recovery rates and mixing strategies, these systems aim for “low incremental salinity” discharge rather than highly concentrated brine streams, leading some developers to describe their goal as “non-toxic brine discharge.”
From a rigorous standpoint, deep-sea desalination systems do not eliminate concentrate discharge altogether. Instead, by controlling salinity levels, discharge depth, and dispersion conditions, they have the potential to significantly reduce the ecological pressure associated with nearshore brine disposal.
A Technological Frontier, Not Yet a New Standard
It is important to note that subsea and deep-sea desalination remains in the demonstration and early commercialization phase. Current activity is limited to a small number of pilot projects and planned demonstration plants.
In terms of global desalination capacity, land-based seawater reverse osmosis continues to dominate. Deep-sea solutions should therefore be viewed as a frontier or complementary technology, targeted at specific scenarios such as land-constrained coastlines, energy-intensive operating environments, or specialized industrial water demands.
Looking ahead, the desalination industry as a whole is evolving along several clear trajectories: improved energy efficiency through advanced membranes, energy recovery devices, and process integration; greater modularity and scalability, enabling flexible deployment from small distributed systems to large modular plants; more environmentally responsible concentrate management to meet increasingly stringent regulatory requirements; and enhanced adaptability to diverse operating conditions, including high salinity, elevated temperatures, complex contaminant profiles, and challenging marine environments.
Within this broader framework, subsea and deep-sea deployment represents one important direction in the industry’s pursuit of more energy-efficient, space-efficient, and environmentally conscious desalination solutions. Whether it will ultimately become a mainstream or standardized approach will depend on the accumulation of long-term operational data and further project experience.
The cases and technical data referenced in this article are based on publicly available industry reports and company disclosures. They are intended solely to illustrate technological development trends and do not constitute commercial endorsement or performance guarantees for any third-party solutions.