I have converted a few 773b haul trucks to water trucks. To operate was pretty basic. Fill with water, turn on the water pump, Usually driven by a hyd motor and hyd pump. Turn on the spray heads. The ones i did were electric solenoids that opened an air valve that held the spray head open. The 4 across the back could be opened individually.
Some trucks have a water cannon on the top or front. some are manually operated and some are remotely operated.