Groundwater is water located beneath the Earth's surface in porous rock and sediment. It originates from rainfall and snowmelt that filters underground, and eventually makes its way back above ground in streams, lakes, and oceans. Groundwater accounts for 1% of the water on Earth but makes up 35 times more than surface water in lakes and streams. It occurs everywhere but is usually found within 750 meters of the surface, and there is enough groundwater to cover the entire Earth's surface in a 55-meter thick layer.