Like sugar and some papers, alcohol-based fuel is hygroscopic
. A hygroscopic substance is one that can readily absorb water from the environment, including from moisture in the air.
Because nitro fuel contains methanol it is hygroscopic. To keep moisture out, it should be stored in a dry location in sealed containers.
Nitro Fuel Storage Tips
If you notice water droplets on the inside of your nitro fuel bottle, it's because the fuel is hygroscopic and probably was left open or not sealed tightly and the nitro fuel absorbed moisture from the air. Moisture can ruin your nitro fuel.