Berlin is located in a dry region of Germany and water supply is a hot topic each summer. That's why the city is adopting measures to absorb and store rainwater like a sponge and release it when water is needed.

But how exactly does that work?

The first step was to build several massive underground overflow basins. They work like huge wastewater parking lots. When it rains, water from the surrounding area is collected in the basin and then pumped to a treatment plant.

Nine of these facilities have already been completed, including one under Mauerpark, a popular hangout spot in the district of Prenzlauer Berg, where parts of the Berlin Wall once stood.

The largest inner-city wastewater basin is still in the making. It will be more than twice the size of the one at Mauerpark. At 30 meters (98.4 feet) deep in the ground, the circular concrete basin will hold nearly 17,000 cubic meters of rainwater once it's completed by 2026. That's equivalent to almost seven Olympic-sized swimming pools.

When there's heavy rain and Berlin's sewage system is at risk of running over, surplus water is stored in the basins. It's then pumped into a purification plant before being released back........

© Deutsche Welle