25% will not hurt the engine. Ethanol hides water though, be diligent and follow the well know guidelines.
Do not store fuel, buy it and use it
Do not store in direct sunlight. it is photosensitive.
Avoid stored fuel temperature changes as this causes condensation.
Avoid pouring from container to container, this will cause octane loss.
If you use ethanol and detect water in your aircraft fuel system it has reached the point of saturation to cause phase separation. Don't just drain off the water; the fuel has gone bad: drain all the fuel and put it in your sons car.
