ethanol is an alcohol and is soluble with water.
gasoline is hydrocarbon based and does not mix with water.
gasoline mixed with ethanol tends to separate when water and condensation gets into the mix.
ethanol tends to be acetic and eats up the lining of the tank and the hoses.
flex fuel cars are designed to deal with theses issues.
fuel pumps don't like water, restrictions in the fuel lines, or clogged fuel filters.