This is a piece of a lithium camera battery dropped in water:
YouTube - Disposable lithium battery strip reacting in water
Here is another lithium battery cut up and dropped in water.
YouTube - danger, flames, water and lithium? interested yet?
Non of these batteries are running away; they are cold. Does this work the same for Lithium Ion, other Lithium polymer batteries? If an electronic devise is shorting out you may be ok if it has not ruptured. Do you know it has not?
What do you do when this happens to passengers in the back and you don't find out till you see or hear a ruckus. Do you throw water on it?:
YouTube - Lithium Ion battery fire
No I am not confident of the answer.