Asking this question seems a bit redundant. Water does not burn, who knows. But why water does not burn, is a question that is not easy to answer.
To answer this question clearly, we must first understand what combustion is?
Usually, combustion is the chemical reaction of substances with oxygen. There are substances that, even at room temperature, ignite when exposed to oxygen. White phosphorus is an example. There are other substances such as coal (mainly carbon), hydrogen, and sulfur, which at normal temperature do not react with oxygen, but when the temperature is increased, they will ignite.
Water is made up of two elements hydrogen and oxygen.
From the outside, alcohol, gasoline, kerosene, and water are all transparent liquids, very similar. But alcohol is made up of three elements carbon, hydrogen, and oxygen, while gasoline and kerosene are made up of two elements carbon, hydrogen. Most carbonaceous substances are combustible.
Alcohol, gasoline, and kerosene have one carbon atom combined with two oxygen atoms to form a carbon dioxide molecule. The hydrogen atoms, on the other hand, combine with oxygen to form water molecules, and so the compounds above burn clean.
By now, you all know why the water doesn’t burn. Water is made up of two elements, hydrogen and oxygen , as a result of the combustion of hydrogen. Since it is a product of combustion, of course it cannot be able to continue to combine with oxygen or in other words it cannot burn again. By the same logic, carbon dioxide is the end product of combustion so carbon dioxide cannot burn anymore. Because carbon dioxide cannot support combustion, and has a heavier density than air, carbon dioxide is used to put out fires.
Of course, there are also many types of matter that cannot be combined with oxygen, no matter how high the temperature is, they are just “good friends” of oxygen. These substances are non-combustible.