Vienna is constructing the world's largest closed drinking water reservoir in Neusiedl am Steinfeld, Lower Austria.

Once completed, the facility will hold an impressive one billion liters of water, enough to submerge the iconic St.

Stephen's Cathedral.

The project, set to finish by 2029, is a response to rising water demand due to climate change and urban growth, which is expected to increase consumption by 15%.

Currently, Vienna uses one billion liters in just two and a half days.

The reservoir will also enhance the city's resilience to crises and help manage extreme weather fluctuations.

Mayor Michael Ludwig emphasized the importance of this "lighthouse project" for Vienna's future security and sustainability.