Bilbao anticipates water with a digital twin of its sewer network.

Locals call Bilbao “el bocho” — the hollow: a valley ringed by mountains and cut through by the Nervión estuary. That geography is its greatest hydraulic challenge. Atlantic rainfall, increasingly intense, falls on hemmed-in terrain whose only outlet is governed by a tide that can vary by up to six meters between high and low water. Beneath the city runs a sewer network whose layout dates back to the 19th century: 740 kilometers of sewers at depths of thirty to forty meters, with stretches crossed by other utilities and plans that don't always match the buried reality. For decades, managing it meant reacting: a static inventory and decisions based on experience, acting once the problem had already surfaced. More than twenty years ago, the City Council asked a far more ambitious question: how to know, before it happens, what will fail and where.

The commitment to digitalizing the water cycle began in 2003 and took a leap forward when ACCIONA came on board: more than ninety field sensors and a digital ecosystem, the NETWIN platform, which brings together in a single environment the network's sensors, the municipal mapping, the pumping-station SCADA, the Nervión tides and weather data. At its core runs Autodesk Water technology. InfoWorks ICM builds the mathematical model of the network; ICMLive feeds it with real-time data, calibrates it and simulates its behavior, generating a digital twin that not only shows what is happening but predicts what will happen — up to 24 hours ahead in critical events. The result is a paradigm shift: from reactive management, acting on the failure, to predictive management, getting ahead of it.

A digital twin is only worth as much as the decisions it enables. In Bilbao those decisions take physical form: sewers replaced, gates installed and storm tanks sized to the capacity the network needs. The model identifies the points where, at high tide or in heavy rain, a sewer could collapse — for instance, through infiltration near the estuary — and makes it possible to remove the risk before it surfaces. It also guides the gradual rollout of separate systems, which split foul water from stormwater, and the simulation of pollutant dispersion: two levers for returning water quality to the Nervión estuary. With the network's health maps, ACCIONA and the City Council prioritize investment according to where the greatest risk and the greatest return lie, and have already designed twenty-seven catchment master plans.

What happens beneath Bilbao anticipates what thousands of cities face. Europe's sewer stock is ageing faster than it is renewed, and the climate adds pressure to networks that were never designed for it. The new EU Urban Wastewater Treatment Directive (2024/3019) requires integrated management plans, tighter control of overflows and progress towards an energy-neutral sector by 2045. The master plans Bilbao is developing with the digital twin connect directly with those requirements: they anticipate the regulation rather than chase it. And the approach is replicable — every city has its own geography, but the method and the technology travel — something ACCIONA is already extending to other networks in Spain and beyond.

Three hundred and fifty thousand residents take for granted that water disappears down the drain once they've used it, and that the streets don't flood when it rains. Behind that normality lies technical work that is almost never seen and only noticed when something fails. Bilbao shows that digitalizing sanitation is not a promise for the future but an operational change already under way, with measurable results. And that it works when it is backed by an administration that believes in it, an operator that builds it into the way it works, and a technology provider that makes it possible. As the City Council puts it, digitalization is not an expense: it is the investment that makes anticipation possible.