Groundwater is water that is found underground in cracks and spaces in soil, sand and rocks. The area where water fills these spaces is called the saturated zone . Groundwater can be found almost everywhere. Heavy rains or melting snow may cause the water table to rise, or an extended period of dry weather may cause the water table to fall. The speed at which groundwater flows depends on the size of the spaces in the soil or rock and how well the spaces are connected.
Aquifers typically consist of gravel, sand, sandstone, or fractured rock, like limestone.
These materials are permeable because they have large connected spaces that allow water to flow through. Water in aquifers is brought to the surface naturally through a spring or can be discharged into lakes and streams. This water can also be extracted through a well drilled into the aquifer. A well is a pipe in the ground that fills with groundwater. This water then can be brought to the surface by a pump.