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Meet the drones patrolling Barcelona's sewers

The largest city on the Mediterranean Sea sits on giant flood-battling rainfall tanks, patrolled by drones to see what's going on in the sewers.

An Aqualogy drone like the unmanned vehicles saving Barcelona's utility workers from getting their feet wet. Rich Trenholm/CNET

BARCELONA -- When you think of drones, you probably think of robot vehicles soaring high over our heads. But there are plenty of hard-to-reach places that aren't out in the open where drones can give you eyes and ears -- and one example is the underground water tanks of Barcelona, Spain, where drones are being sent in to patrol the pipes.

The company behind the pilot scheme is Sociedad General de Aguas de Barcelona (SAGB), originally formed back in 1867 to provide water to the Catalonian capital. Under the Aqualogy brand, the company is offering various innovations to water companies around the world, from remote meter reading to apps that tell you the water quality at the beach before you don your bathers -- to drones heading under the streets of Barcelona itself.

Barcelona is the largest metropolis on the Mediterranean Sea and doesn't typically get much rain -- but when it rains it pours. That can overwhelm the water removal infrastructure and flood the city, and because Barcelona has a unitary water system -- waste water and rainwater travel through the same pipes -- untreated sewage can end up contaminating the sea.

To prevent flooding, the city has, since 1997, built 13 giant underground water retention tanks that hold on to the overflow rather than unleashing pollution into the sea. They prevent 940 tonnes of suspended matter pouring into the Mediterranean each year.

Currently, visual inspection and maintenance of these tanks and pipes requires workers to head underground. But in a test project, unmanned aerial vehicles have been taking on the task, steered remotely by an operator watching a feed from the drone's cameras as they pilot it through the pipes. It's a dirty job, but somebody's got to do it -- and with a drone's help, a worker can do it without even stepping into a pair of wellies.