You already know what water is. This page explains some other information that you might not know.
Pure water is H2O, but since there are many different sources of water, the water usually has extra minerals or chemicals depending on the source.
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The boiling point is the temperature at which water converts into vapor and starts bubbling like crazy. The reason this is important is because once that point is reached, water cannot get any hotter, meaning your food will cook slower or faster based on what the boiling point actually is.
The boiling point of water is 212 degrees F at sea level, but when the atmospheric pressure rises or drops depending on the altitude, the boiling point changes by 2 degrees for every 1000 feet. For instance, if you live 5000 feet above sea level, the atmospheric pressure drops and causes the boiling point to drop by 10 degrees, making the boiling point only 202 degrees.
Water freezes at 32 degrees F.