Is it possible to burn water?
No, water is already the result of burning Hydrogen in Air (Oxygen). The burning process is a combustion reaction involving Oxidation, in this case, the Oxidation of Hydrogen; (Water is Hydrogen Oxide). Oxygen itself does NOT burn but is necessary for combustion to occur. (The effect you saw with Potassium was the Hydrogen evolved from the reaction that was burning). (There is one experiment which SEEMS to indicate that water will burn but, it’s a trick. Drop a battery into a glass of tap water. Bubbles of gas are seen coming from around the battery. This is Hydrogen from the electrolysis of the water. As it comes off the surface of the water, it can be ignited making it LOOK like the water is burning).