The first elements to form at the beginning of the universe were 92% hydrogen and 8% helium, with the exception of a very small amount of lithium. The remaining elements were formed by stellar nucleosynthesis. That is, by the fusion of the stellar core, or by the heat of an explosion at the star’s death. As a result, oxygen became the third largest element in the universe. So naturally there was more opportunity for oxygen and hydrogen to meet anywhere in the universe. Therefore, water is the most abundant compound in the universe.