When it snows we complain that we have to shovel the snow and clean it off our cars. We worry about driving conditions and are afraid we might fall on the ice that accompanies the snow. But if we wait a few days, the temperature will rise, and it will all melt and be gone. When it rains we complain that we are wet, that our roof is leaking or that there is flooding. But wait a few hours or days and the puddles dry up, the leak stops and the water recedes. And then when it doesn’t rain we complain that the plants are dying and the water table is low. But wait a few days and there will be rain. This is all brought to us by the beauty of STATES OF MATTER.
Matter, and especially water changes state every second, every minute, every hour of every day on planet Earth.
Changes in state are all about energy, specifically heat energy. If we add energy (heat) to a solid, such as ice, we get water. If we keep adding more heat, we get a gas, water vapor. To reverse the process we reduce the amount of energy and the gas becomes liquid again, and then a solid if the temperature is cold enough.
My favorite phase changes are sublimation and deposition. It is possible to go from a solid to a gas, this is called sublimation, and from a gas to a sold, this is called deposition. An example of sublimation is dry ice (frozen carbon dioxide). When dry ice is placed at room temperature, it changes from a solid to a gas, and skips the liquid phase. An example of deposition is the thin film of ice that forms on window during winter months.
For more information on changes of state of matter check out:
Science is My Specialty 
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