Ethanol absorbs water anyway, do you want 3 gallons of gas with water in it or 18? I have personally done this for 20 years and my dad did the same with his 1983 Mustang 5.0 he had for an additional 10 past that. They'll run in the spring and then you have fresh gas right away because you go right to the gas station after the car warms up. I'd be more worried about the gas spoiling than the water in most places.