A desalination plant has two critical points underwater: the intake through which seawater enters, and the diffuser through which the brine is returned. Maintaining both is commercial diving work, and the main risk isn't depth but the pressure differential of an intake in service.
Desalination has stopped being a Mediterranean quirk and become basic infrastructure across much of the world. And every desalination plant, whatever its size, has the same pair of weak points: on one side it draws in seawater, on the other it returns a brine that's denser and saltier than the sea around it. Both ends are submerged.
That's why there's a niche of underwater work tied to desalination, and why it's a stable one: the plant can't stop for long, the intake fouls itself, and the diffuser is exposed to currents and bed-load. Someone has to go down and check it regularly.
It's civil and industrial work, with surface-supplied diving and usually moderate depths. It has nothing to do with saturation diving, but it shares something important with offshore: procedural discipline, because here a mistake costs just as much.
What's underwater at a desalination plant
The intake
There are two approaches. An open intake draws water directly from the sea through a pipeline ending in a tower or a submerged mouth, protected by screens. A closed, or indirect, intake takes water filtered through the ground, via wells or buried drains under the seabed, so the sea never comes into direct contact with the pipeline.
The difference matters a great deal for the diver. An open intake has submerged structure to inspect, clean and repair on a recurring basis. With an indirect intake, underwater work is much less, almost limited to monitoring the seabed and checking there's no scouring or surface silting. When someone says they work on desalination plants, they're almost always talking about an open intake.
The tower and the screens
The intake mouth is usually raised above the seabed to avoid drawing in sediment, and is protected by screens that serve a dual purpose: keeping objects out and limiting the water's approach velocity to reduce organism entrainment. These screens are the element that needs the most maintenance, since they foul up with marine growth, algae and whatever the sea washes in after a storm.
The brine diffuser
Brine is denser than seawater, so if simply discharged it tends to sink and form a hypersaline layer on the seabed. To prevent that, a diffuser is used: a final stretch of pipe with several nozzles angled so the jet mixes quickly with the receiving water. How well the diffuser performs depends on the nozzles being clear, angled as designed and undamaged.
Checking this is a classic inspection task, and it also has an environmental dimension: how the discharge behaves is usually subject to permit conditions, and inspecting the diffuser is part of the evidence that the plant is meeting what it promised. It's the same kind of work done on submarine outfalls and water intakes, with the added factor of the density of the discharged fluid.
The risk that defines this work: suction
If there's one concept to take on board before approaching an intake, it's this. An intake pipeline in service is drawing a large flow through a limited cross-section. Any object that gets close to that mouth is subjected to a drag force that grows very fast as the distance shrinks, and against which you can neither swim nor be pulled free from the surface.
This isn't an abstract risk or a textbook precaution: it's the scenario that kills at this type of facility, just as the pressure differential does at gates and locks. A diver trapped against an intake screen isn't freed by force; they're freed by stopping the pump, and for that someone needs to be able to stop it within seconds, with it agreed beforehand exactly how.
The control here is procedural and follows an order that allows no shortcuts. First, identify every line drawing from or discharging into the area, including ones that are out of service but could start automatically. Second, physically stop and lock out that equipment, with interlocking and tagging, and with the key held by whoever is running the operation, not the plant operator. Third, confirm in the water that there is indeed no flow before approaching. And fourth, agree in advance how an emergency stop will be communicated.
Working with the intake running while keeping a safe distance is a practice that does exist, but it requires a specific analysis justifying that distance and a strong reason not to shut down. The default option, and the one worth insisting on, is to lock out.
The other risks specific to a plant
Chemical dosing
Many plants dose chemicals into the intake to control biological growth, sometimes continuously and sometimes in occasional shock doses at higher concentration. A diver entering the water during or just after a dosing event can be exposed to a chemical without knowing it. This is dealt with by including it explicitly in the permit to work: what's being dosed, when, and written confirmation that it has stopped.
Fouling and visibility
Intakes are an excellent habitat: moving water, a constant food supply and a hard surface. Colonisation is fast and dense, and cleaning it off is a major part of the job. It's done with pressure water or mechanical tools, following the same logic as biofouling cleaning on hulls, but with the constraint of not damaging screens or coatings.
That cleaning drops visibility to zero straight away, so the method has to be planned for working blind: fixed reference points, guide lines and an agreed sequence so as not to lose orientation inside a structure full of gaps.
Espacios confinados
The inside of an intake pipe or a pump chamber is a flooded confined space. Going in there isn't just another dive: it needs a specific procedure, entry control, a continuous lifeline and a rescue plan that's realistic rather than a statement of intent. Many companies simply don't do it, and instead handle the inspection with a camera or a vehicle, which is usually the right call.
How a campaign is organised
The starting point is agreeing a shutdown window with the plant. A desalination plant has production commitments and sometimes supplies an urban network, so the availability to stop a line is limited and has to be negotiated weeks in advance. It's usual to work line by line if the plant has redundant intakes, which allows partial production to continue.
From there, the sequence follows any serious industrial inspection: general survey, selective cleaning of the areas to be assessed, detailed inspection with photographic record, measurements where relevant, and a report that separates what's urgent from what can be scheduled. The same visual inspection levels apply here, from general survey through to detailed inspection, as on any other structure.
The deliverable is what the client is paying for. A plant needs to know whether the head loss it's seeing at its intake is down to a clogged screen, sediment build-up in the pipeline or structural damage, because each cause has a different remedy and cost. Answering that with evidence is where the work adds value.
What gets repaired and what gets replaced
Part of the job is solved just by cleaning, and it's worth not underrating it: recovering the free area of a clogged screen can restore pumping performance the plant had been losing for months, and it's the intervention with the best cost-to-benefit ratio of all a desalination plant's underwater maintenance.
Above that come the structural repairs: replacing lengths of screen and their fixings, renewing cathodic protection, repairing concrete on towers and chambers, and repositioning or replacing diffuser nozzles. All of this is done underwater with conventional submerged-works techniques, almost always with the relevant line out of service.
What rarely gets solved this way is a design problem. If an intake is chronically drawing in sediment, or a diffuser isn't diluting as it should, the diver can document the symptom precisely, but the solution lies in engineering and construction work, not more maintenance. Recognising that boundary and saying so in the report is part of the job.
Who does this work
A commercial diver on surface-supplied diving with a qualification valid in the country where the work is taking place. No saturation certificationis required, and depth is rarely the limiting factor. What is valued is experience in industrial work with equipment lockout, being comfortable in zero visibility, and the ability to document.
It's a niche usually reached from port and marine-works diving, through underwater services companies that already work for industrial clients. If you're starting out, the route runs through a recognised school and getting into a company with this kind of contract; you can get a feel for the sector from the list of commercial diving companies.
Frequently asked questions
Can you dive in an intake while the plant is running?
As a rule, no. The suction flow creates a drag force a diver can't fight, so the correct approach is to physically stop and lock out the equipment before getting close. Working with the intake active is only considered while keeping safe distances justified by a specific analysis.
What is the brine diffuser and why is it inspected?
It's the final stretch of the discharge, with nozzles angled so the brine mixes quickly with the seawater instead of building up on the seabed. It's inspected to check the nozzles are clear, intact and angled as designed, since the behaviour of the discharge depends on it.
How deep is this kind of work?
Usually moderate. Intakes and diffusers sit at the distance and depth needed to draw in clean water and let the discharge dilute properly, but rarely at depths requiring techniques other than surface-supplied diving.
Is there a chemical risk for the diver?
There can be, if the plant is dosing chemicals to control biological growth in the intake. That's why dosing has to be identified and stopped before the dive, and it must be stated explicitly in the permit to work, alongside pump lockout.
Do all desalination plants need divers?
Not to the same extent. Plants with an open intake have submerged structure that needs recurring maintenance. Those that draw water through wells or drains under the seabed generate much less underwater work, mostly limited to monitoring the seabed and the discharge point.
Published 6 September 2026 · By Arthur More, professional saturation diver
Photo: Wonderlane · CC BY via Openverse