[damage]

You will find that any fuel that has any form of ethanol octane boost will be susceptible to absorbing water. Both methanol and ethanol are derived from the same source and both are hydroscopic which means as well as breaking down completely in water they will also suck water in from the atmosphere.

Unleaded fuel is hydroscopic because various hydrocarbons are added to enhance the octane.

Any fuel tank that is left for any extended period of time half empty will breath with atmosphere conditions and if the humidity is high as in Cairns then the continual exchange of air will lead to an increased water content into the fuel.

Easy way to stop this in both cars and boats when you put them away do it with a full tank of fuel and this removes the breathing room in the tank and decreases the chance of fuel contamination.

Of course this is all dependent on how well your local servo manages their tanks.