Well, there's plenty of improvement options left. One them would be your idea. Another one would be an improved 'rapid deployment' command, so a 5th fire fighter automatically installs a water supply line (hydrant to engine). That one would be great for American mods, because most American fire engine's do not have a water tank at all (right? ), so you will HAVE TO to install a water supply line before you can use any hoses or the deck gun to maintain this level of realism.
Not quite right Hoppah. American fire engines have a LIMITED tank. Usually somewhere between 500 and 1000 gallons. Many times the tank is equal or smaller than the pump capacity (i.e. 1250 gpm (gallons per minute)). This allows for a truck to fast attack a small fire (garbage / car) without having to first connect to a hydrant, and give the crew a little time to get the hydrant line connected.