There are several theories about how Earth acquired its water, but the most widely accepted one is that it was delivered by comets and asteroids during the early stages of its formation. Comets and asteroids are made up of ice and other volatile materials, and they are thought to have collided with Earth frequently during the late stage of its accretion, contributing to the planet's water supply.

Another theory suggests that water may have originated from the Earth's interior. Volcanic eruptions and hydrothermal vents may have released water vapor into the atmosphere, which eventually condensed and formed oceans and other bodies of water.

It is also possible that a combination of these processes contributed to Earth's water content. Over time, the water on Earth has been recycled through the atmosphere, oceans, and land through the process of the water cycle.