Water is a molecular compound that is a liquid at a certain temperature and pressure. It is a very important molecule because without it humans and plants and animals wouldn't be able to live because all living life needs water to survive. It's chemical formula is H20 which means that a water molecule has 2 hydrogen atoms and 1 oxygen atoms. Water can change into vapor when it boild and ice when it freezes. About 97 percent of the earths ocean is saltwater which is undrinkable. This is what a water molecule is.