Groundwater is water that is moving inside rocks. A rock that allows water to move through it is called an aquifer.

The main rocks where you will find useful amounts of water are limestone (including chalk) and sandstone.

People dig wells to these rock layers, even when they are tens or hundreds of metres below the ground surface. Wells give reliable water in areas that do not have rivers, and are widely used for drinking water and by farmers in almost all countries.

However, there can be problems with some groundwater, because there are too many minerals concentrated in them. Spring water is normally quite safe, but the problems are more likely to occur with deep groundwater pumped up, as the video shows.