Methanol is what they call hygroscopic which just means it'll keep on attracting moisture from the air almost without limit. This is why you should never leave a container of fuel open any longer than necessary and must be sealed completely air tight. For the same reason, never leave any fuel in the tank before putting the model away and always run the engine completely dry at the end of every day's flying. Nitro will only absorb up to a maximum of 2.5% water but methanol will absorb 100%.