You are looking at about 450,000 gallons of water, going up 100 feet in the air.
NASA uses this system to reduce extreme heat and energy generated by a rocket launch.
This specifically is the Ignition Overpressure Protection and Sound Suppression water deluge system at Kennedy Space Center's Launch Pad 39B.This particular test was done in 2018 as part of the preparation for launching the Space Launch System rocket on Exploration Mission-1 and subsequent missions.