As South Carolina struggled this week not only with floods, but also with a shortage of drinking water, Atlanta leaders worked to make sure if a disaster strikes here, the city will have a backup water supply.

The backup supply will be in Bellwood Quarry – which is currently a giant hole in the ground just north of Bankhead. Eventually it’ll be a reservoir, holding enough water to get Atlanta through 30 days if something happens to the regular water supply. The land around it will become the city’s largest park.

At a press conference held at the bottom of the quarry on Wednesday, Mayor Kasim Reed said the project will change the city.

“It will expand green space in the city of Atlanta. It will expand park space in the city of Atlanta,” Reed said. “And it will meet one of the most crucial threats facing the city, and that is a lack of access to clean drinking water in the event of crisis.”

Atlanta’s Department of Watershed Management expects to start filling the former granite quarry with water in 2017 and to finish the reservoir in 2020. Right now, a company in Ohio is building a machine that will dig a five-mile-long tunnel to get water to and from the quarry.