Here's why:

* The Big Bang: This event, approximately 13.8 billion years ago, is the origin of all the matter in the universe.

* Early Universe: Immediately following the Big Bang, the universe was incredibly hot and dense. This heat and density allowed protons and neutrons to form from the initial energy.

* Hydrogen Formation: Protons are the nuclei of hydrogen atoms. In the first few minutes after the Big Bang, these protons combined with electrons to form hydrogen atoms.

* Water Formation: Hydrogen atoms, along with oxygen atoms (which were also formed later in stars), eventually came together to form water molecules.

So, while water itself is formed through various processes throughout the universe's history, the hydrogen atoms within it originated from the very beginning of the universe.