It’s called the Hydrologic Cycle.
Water in the air is called vapor, when it comes together in a form we can see that is called condensation. This forms clouds. The water then comes down as precipitation ( rain, snow, sleet, hail). This water then falls into bodies of water (oceans, lakes, rivers, streams) or the water falls to the ground. That water either runs into bodies of water or is absorbed into the ground. The water in the ground is either taken into the roots of plants or seeps down further into the ground. There is a layer of porous rock called the aquifer. The water gathers there forming something like underground lakes. This is called groundwater. This water is either brought up by us through wells or comes out on its’ own through springs. The water that is absorbed by plants travel through the plant and is expelled through their leaves this is called transpiration.
And when the water in the bodies of water like River, lakes, streams, rivers, ponds is heated by the sun is becomes water vapor AGAIN. Starting the whole process over AGAIN.
There is no new water on Earth. The water we have today is the same water that has been here from the beginning of time. That water in your store bought bottle was dinosaur pee at one time. ;)