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Submerged towers, pipelines in the Mediterranean, and a plant in El Prat de Llobregat form one of Spain’s main desalination structures, created to reinforce Barcelona’s water supply amid pressure on reservoirs, rivers, and aquifers.
Installed on the Mediterranean seabed, two towers draw seawater 2.2 kilometers off the coast of Barcelona and supply the Llobregat desalination plant, a facility capable of producing up to 200 million liters of drinking water per day in El Prat de Llobregat, in the metropolitan area of the Catalan capital.
Created to enhance local water security, the structure is part of the public Ter-Llobregat system and serves an area marked by high urban concentration, high consumption demand, and recurring pressure on rivers, reservoirs, and aquifers.
How Mediterranean water reaches the desalination plant
Far from the shoreline, the intake occurs in a submerged area where two towers extract seawater at a depth of 30 meters, reducing the system’s exposure to common interferences in areas closer to the coast.
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After entering the underwater structures, the water travels through two conduits of 2.2 kilometers to a pumping station located on the beach, responsible for propelling the captured volume towards the industrial plant installed near the mouth of the Llobregat River.
From there, a terrestrial pipeline of about 3 kilometers runs parallel to the sea, passes under the Llobregat River, and carries the raw water to the treatment unit, as described by ATL, the public company of the Ter-Llobregat system.
Between the Mediterranean seabed and the urban network, this technical corridor shows why the work goes beyond the visible image of a land-based plant, as an essential part of the infrastructure remains hidden under the sea and underground.
Capacity equals 200 million liters per day
At maximum daily capacity, the facility produces 200 thousand cubic meters of desalinated water, a volume equivalent to 200 million liters, as each cubic meter corresponds to a thousand liters within this conversion used in supply.
Over the course of a year, the plant can add up to 60 cubic hectometers to the public system, a number adopted by the Catalan Water Agency and ATL as the operational reference for the Llobregat desalination plant.
This volume, however, does not come from the sea ready for consumption, because the captured water needs to undergo pumping, pre-treatment, filtration, reverse osmosis, remineralization, and final quality controls before being distributed.
In the industrial stage, the saltwater goes through a rigorous sequence to remove particles, protect equipment, and separate dissolved salts until it reaches the necessary conditions to be incorporated into the system that supplies Barcelona and nearby municipalities.
Reverse osmosis transforms saltwater into potable water
At the center of the operation is reverse osmosis, a technology in which water passes through membranes capable of retaining a large part of the salts and other components naturally present in seawater.
Before this phase, the captured volume undergoes preliminary treatments to reduce impurities and suspended materials, as accumulated particles could impair system performance and increase the need for equipment maintenance.
With the separation completed, the operation generates two streams: one of desalinated water, directed for final adjustments, and another of brine, a waste with a higher concentration of salts that requires its own infrastructure for controlled disposal.
The efficiency of the process depends on the pressure applied, the quality of the pre-treatment, and the condition of the membranes, factors that make desalination a complex technological solution, even when the result appears to the consumer simply as water from the tap.
Barcelona strengthens supply with seawater
For Barcelona and neighboring municipalities, the Llobregat desalination plant has a strategic function because it reduces the exclusive dependence on rivers, reservoirs, and aquifers, especially during periods of drought or increased urban demand.
In Mediterranean regions, structures of this type have gained relevance due to the combination of high consumption and irregular supply of fresh water, a scenario that leads governments to diversify sources without abandoning management, economy, and loss control policies.
The metropolitan area concentrates population, services, economic activities, and tourist flow, factors that increase the need for systems capable of maintaining supply even when traditional water sources face critical moments.
In this context, seawater functions as a complementary source, without eliminating the need to preserve rivers, reduce network losses, or encourage rational use, but expanding the public system’s response margin in scarcity situations.
Submerged Structures Sustain the Megacenter
Due to the scale of the installation, the production of potable water depends on underwater towers, long pipelines, pumping station, filtration systems, membranes, and internal reservoirs, elements distributed between the sea, the beach, and the plant.
Although the industrial unit concentrates the final stages of treatment, the process begins kilometers from the coast, in an area where engineering needs to operate continuously under marine conditions, with flow control and specialized maintenance.
This characteristic differentiates desalination from other forms of supply, as the water source is voluminous but requires energy, technology, environmental licensing, and integration with a network capable of distributing the treated product to the served cities.
In Llobregat, the intake at 30 meters deep and 2.2 kilometers from the beach shows how urban supply has also come to depend on works invisible to most of the population.
Why the Project Draws Attention Outside Spain
By combining the Mediterranean, underwater pipelines, and production of hundreds of millions of liters per day, the Llobregat desalination plant has become an example of large-scale water infrastructure in a densely populated region.
With easily measurable numbers, the project transforms saltwater into a regular source for the public system and connects the marine environment, industrial technology, and urban supply in a single operation.
Even so, desalination does not replace broad water planning, as its use needs to coexist with watershed conservation, loss control, water reuse, and demand management, especially in areas vulnerable to prolonged droughts.
Under the Catalan coast, submerged towers and giant pipelines reveal that the water consumed in large coastal cities can take a more complex path than it seems, starting at the bottom of the sea before reaching urban distribution networks.
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