Water on Earth primarily comes from two sources:
- Water was delivered to Earth by water-rich space objects such as asteroids and comets early in Earth's history. Carbonaceous chondrites, a type of asteroid, closely match the isotopic composition of Earth's ocean water, suggesting they are a major source of Earth's water. Some water may also have originated from the planet's interior, where hydrogen interacted with minerals and was released through volcanic activity.
- Earth's water exists today in liquid form mainly because the planet is at a suitable distance from the Sun, known as the habitable zone, which allows water to remain liquid rather than freezing or evaporating into space.
In addition to these origins, the water we use daily often comes from natural surface sources like rivers, lakes, and groundwater that have undergone treatment before distribution. Thus, water's origin is a combination of delivery by extraterrestrial bodies and geological processes within Earth, sustained by Earth's location in the solar system.
