The vast majority of water in fuel/condensation happens before you pump it into your can. The amount of ethanol the fuel contains is determined right as it goes into the holding tank at the station, the driver mixes it as he fills the gas stations tank. He dips the tank for level, determines it needs 25,000 gallons and based on that number, figures out how much ethanol to add. He never tested the tank to see how much water or ethanol it already had.... why you test the fuel before adding it to your can. The can you have stored in the shed can no way condense an extra pint of water or change the ethanol content... your doomed from the beginning, especially if the tank is low and why it's good to use a filling station with a high amount of sales.... so it's consistently being emptied.
Like Neal said, adding a stabilizer is good, but determining if your filling station is killing you is the CORRECT answer... before you pump it!
OR buying non-E fuel.