Water contains two types of elements, hydrogen and oxygen, and three atoms in total. Because hydrogen is the most abundant element in the universe and oxygen is also common, water is thought to be a common chemical throughout the universe.
Stars are initially comprised almost exclusively of hydrogen, and many stars form oxygen as they fuse elements. When two hydrogen atoms bond with an oxygen atom, a molecule of water forms. Water exists in abundance on Earth and is believed to be abundant on Uranus as well. It is also found on the moons Enceladus, Europa and Titan, and it covers the surface of comets.