一是水碰到炙热 (zhì rè)的物体就会变成水蒸气，带走物体上的热能，降低温度；
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Why is water a nemesis to fire?
For fire to start, we have to know that fire requires a certain temperature for oxidation to occur, resulting in proper fire with flames and all.
Water aids in putting out the fire because of two characteristics:
Firstly, when water is in contact with hot objects, it will evaporate to become steam, taking the heat away from the object thus bringing down the temperature, making it more difficult for the fire to burn.
Secondly, when water evaporates and becomes steam, it occupies a broader surface area, surrounding the area or object that is engulfed in fire. This creates a barrier where the air, especially oxygen, does not reach the fire easily, causing the fire to subside.
Source: Quoted from an educational book.