☔ The youngest groundwater, from a few years to a few decades old, is found in shallow aquifers that are recharged by recent rain events or surfacewater. This groundwater is more susceptible to contamination.

Deep confined aquifers on the other hand can contain much older groundwater, sometimes up to thousands or even millions of years old. The water in these deep aquifers has been isolated from the surface for long periods of time and can have unique chemical characteristics.