Experiment: Cover a burning candle with a glass so that the candle is in an air-tight space with the water at the ground.
Observation: After a while, the candle dims and goes out. Just before the candle dies, the water level rises up into the glass.
Explanation: The candle heats the air and uses up the oxygen in the glass. When oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases, which leads to the rise of the water.