Long before the solar system existed, water was already forming in deep space.

In vast, frigid molecular clouds, tiny dust grains acted like microscopic workbenches. Hydrogen and oxygen atoms landed on their surfaces, met, and bonded, building water molecules in the cold dark, at temperatures far below anything on Earth. 

When the cloud eventually collapsed to form the Sun and planets, some of that ancient water survived the violence of the process. It became part of the material that formed asteroids, which later delivered it to the young Earth.

Scientists estimate that roughly one-third to one-half of Earth’s water may trace back to this pre-solar origin.

That means some of the water cycling through your glass today began its journey before the Sun existed, drifting through interstellar space, waiting for a planet that didn’t yet exist.