Subsea Reverse Osmosis: why go to the trouble of operating in the deep?

It’s often asked why we would go to the trouble of installing our pods in the deep sea. Clearly there is  free pressure, lots of it, but to pass seawater through a membrane you still need to create a pressure gradient. We also need to then send the water up a vertical distance of 400m to get back to shore. So, by the time you’ve done that do you actually save that much energy? The answer is yes.

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Hydrostatic Pressure: Mountains of Water Above Us

To understand the physics , we need to revisit a simple but powerful principle: hydrostatic pressure increases with depth. For every 10 meters (33 feet) you descend below the ocean’s surface, the pressure increases by roughly 1 atmosphere (14.7 psi). This adds up quickly: at 400 meters, the pressure is already 40 atm; at 500 meters, about 50 atm. For comparison, the osmotic pressure of seawater, the minimum pressure required to counteract the natural flow of water through a semipermeable membrane, is about 27 atm. In other words, the ocean at a few hundred meters depth already exceeds the pressure needed to drive reverse osmosis.

This means that if you place a reverse osmosis module at 500 meters depth, nature’s “mountain of water” above it is already applying the necessary force

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Creating a pressure gradient

Reverse osmosis (RO) occurs when external pressure greater than the osmotic pressure is applied to salty water, forcing pure water molecules across the membrane and leaving salts and other contaminants behind.  

The key reason behind energy saving compared to onshore reverse osmosis is the fact that for the same amount of fresh water we’re depressurizing one molecule rather than pressurizing two. To make these possible, subsea pumps are used to create a pressure gradient across the membrane—otherwise the natural hydrostatic pressure would remain static, and reverse osmosis would not occur.

For comparison, a land-based facility must use giant high-pressure pumps to overcome the osmotic pressure. In contrast, our pods rely on the ocean to provide all of that initial pressure, with subsea pumps acting more like gentle delivery devices rather than energy-hungry drivers. This shift dramatically lowers the energy footprint of the reverse osmosis process, if we pressurize half the water, we use half the energy. Doing it this way around also allows us to:

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a) Safely filter out micro-organisms before experiencing any exposure to the pressure gradient. This forms the basis of our proprietary LifeSafe^TM intake design.

b) Avoid creating a strong brine concentration  

c) Complete the reverse osmosis process without using any chemicals

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More on these points later.

Turning Physics into Technology

Fresh water produced inside the pod is delivered to land through an undersea pipeline. Instead of requiring large pumps to pressurize the saltwater, the system only needs smaller pumps to move the water to shore, making the process dramatically more efficient.  

The benefits are striking:

• Energy savings of approximately 40% compared to land-based RO plants. This is after factoring in convenyence back to shore and friction losses in the pipeline.

• Reduced coastal footprint, since desalination units sit offshore rather than turning beaches into industrial sites.

• Lower environmental impact, as brine (the concentrated saltwater by-product) can be returned to the mid-water column where natural dispersion process reliably even out salinity.  instead of being dumped near fragile shorelines.

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A Natural Partnership

Harnessing the ocean’s own pressure is an elegant example of working with, rather than against, natural forces. By leveraging physics, we can unlock abundant drinking water while minimizing energy demands and ecological harm.

Of course, challenges remain maintaining equipment in harsh marine environments, ensuring membranes resist fouling, and monitoring ecosystems carefully. But the core principle is thoroughly proven.  With thoughtful design, that pressure can help secure humanity’s future freshwater supply, while protecting the building blocks of earth’s food chain.

In many ways, this approach redefines desalination, not as a battle against nature, but as a collaboration with it. Each step forward brings us closer to a model where water security and ocean health reinforce one another rather than compete. If pursued with care, deep ocean reverse osmosis could stand as a blueprint for how technology and ecosystems can coexist in balance, offering resilience to communities facing the growing strains of climate change while maintaining ocean health.

Citations

• Osmotic Pressure Basics: Wikipedia – Osmotic pressure

• Reverse Osmosis Principles: MDPI – Fundamentals of Reverse Osmosis

• Desalination Overview: Wikipedia – Desalination

• Deep-Sea Pressure Desalination Concepts: Scientific American – Deep-Sea Desalination

• Industry Examples: Imnovation Hub – Desalination Pods  

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