Temp definitely comes into play. Nobody nowadays would water down their gas tanks. Think about this: watch your iced tea glass as it sits on a hot day. Condensation forms on the outside of the glass. Now pour hot coffee in a jar half full and sit it in the fridge. You will see condensation on the inside of the jar. Hot inside cold outside= condensation inside. The tanks underground maintain a temp year-round of close to 55 degrees. A tanker truck loaded with hot fuel in the heat of summer unloads 90 degree Gasoline into the underground tank. Hot inside cold outside condensation forms INSIDE !