E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Fire and Water.
I will go through fire and water to serve you. The reference is the ordeals of fire and water which might be transferred to substitutes. Paul seems to refer to substitutional death in Rom. v. 7: Scarcely for a righteous man will one die; yet for a good man some would even dare to die.