I see you are doubling down on belittling the work of others. In an unincorporated area (that is to say a place where erecting a domicile is not supported and yet also not forbidden) the firefighters may not have water for a "water gun," as you say.

If they had access to water, a standoff approach with "a water gun" would only control the fire from spreading more broadly than building and damage the structure through inundation. If the structure was salvable, then the work of a firefighter is to control combustion to extinction using tools to manage the movement of air and other gases so building materials stop burning and do not reignite. It is a close-in effort.