Groundwater and aquifers — Earth science, 11–13 years
Discover how rainwater moves through pores and cracks underground, collects in aquifers and reaches wells and springs.
Water beneath our feet
Groundwater is water stored and moving beneath the land, not a hidden underground river in every place. It fills spaces between grains of sand and gravel, and may occupy cracks in solid rock. An aquifer is a layer or body of rock and sediment that stores and lets useful amounts of water move.
Why does infiltration matter?
People needed to understand why some wells keep supplying water while others dry up or become polluted. Rain can soak into permeable ground, but clay and solid rock may slow or block its movement. Knowing this helps protect recharge areas, where water enters an aquifer, and avoid placing pollution above drinking-water supplies.
A simple water budget
A small aquifer receives 1,000 litres of rainwater each day. Plants and evaporation return 600 litres to the air, and a nearby stream receives 250 litres. That leaves 150 litres to refill the aquifer. If pumping removes 200 litres daily, the stored amount falls by 50 litres per day.
The underground-lake trap
It is reasonable to imagine a huge underground lake, because a well gives water as if it were connected to one. Usually, groundwater is spread through tiny spaces in sediment or cracks in rock, more like water in a wet sponge. Some caves contain pools or streams, but they are not what most wells draw from.
Wells, springs and clean water
Groundwater supplies wells, feeds springs and supports rivers during dry weather. Farmers and towns may pump it for crops and drinking, but pumping too quickly can lower the water table, dry springs or cause land to sink. Protecting recharge areas and testing water quality keeps this hidden supply safer.
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