The USGS Water Science School
Lots of water exists in the ground below your feet. It is called "groundwater" and it gets into the ground when precipitation falls on the land and soaks into the ground.
Plants use groundwater to grow. The water underground is always moving, with most of it ending up back in the oceans.
Sometimes groundwater finds its way back to the land surface, as this picture of water coming out of a canyon wall in the Grand Canyon, USA shows.