Water is heavy
Jearl Walker www.flyingcircusofphysics.com
December 2013 When an air tanker (or water bomber) drops water on the flames of a forest fire, the water is released over several seconds as a spray so as to spread it over as much burning area as possible. That technique also decreases the damage done to the trees and other vegetation. Here is an example in which the spray is used to dampen a truck fire after the truck and a roader grader had collided. Notice that neither the truck nor the grader are noticeably damaged by the released water.
One of these air tankers can release several thousand liters of water, which weighs several thousand tons (or tens of kilonewtons). Had the water simply been poured out of the aircraft, the impact would have been far more severe. Indeed, here is a dramatic example:
Water is heavy!