A water seperator filter is a very good idea. It will not only keep the water out but filter out any foreign objects the ethanol may release. Here is what the most common look like look like: Bass Pro Shops Fuel Filter/Water Separator Kit for Mercury Motors
Or you can get one like this which you can drain the water out of. Racor Gasoline Spin-On Series Fuel Filter/Water Separators & Parts - iboats.com
They are pretty easy to install.