The amount of water needed to keep the battery cool and from exploding is several orders of magnitude more than what is needed for a typical car fire, and also several orders of magnitude more than a fire engine can carry. That means if a Tesla battery catches fire and there isn't a hydrant or sufficient water source that fire fighters can tap into, the car can burn out of control and explode.
You are literally saying that the water requirement is so great it could not be supplied by 10, 100, or even 1000 fire trucks combined. Assuming several means at least 4, then you are saying it would take 10,000 fire trucks worth of water to cool a single Tesla battery fire.
And this is out of over 1 million cars sold globally.
