The Metropolitan Water District of Southern California and the Yorba Linda Water District celebrated today the dedication of a new helicopter hydrant at the Robert B. Diemer Water Treatment Plant – providing firefighters a new, strategically located water source for aerial fire suppression. … The Diemer Helicopter Hydrant holds 8,500 gallons of water and can be continuously refilled in less than 10 minutes via a gravity-fed water line from Diemer Plant’s treated-water reservoir.