Putting out fires in high-rise buildings can pose all kinds of challenges. Beyond using sprinklers inside of the building, it can be very difficult for firefighting equipment to reach floors that are taller than the pressurized fire hoses. So the idea of fighting fires in tall buildings using drones definitely has some merit.
Recently, a company in China performed a live fire drill using drones they programmed to carry fire hoses.
The Guofei General Aviation Equipment Manufacturing Co. used a number of their industrial-strength UAVs to extinguish a fire they set on a practice tower in Chongqing, China. Each drone carries a tank filled with fire suppressant powder, and is connected to a skinny water hose tether. Using this setup, each drone can control fire in up to 100 cubic meters (~3531 cubic feet) of space, and can reach up to 200 meters (~656 feet) off the ground.
The demonstration video is impressive, though I wonder how effective this method would be for fires that are deep inside of a building. Perhaps they could break out a window and fly drones inside using remote cameras?