What is a confined aquifer?

A confined aquifer is defined as a water-bearing geological formation that is trapped between two impermeable layers of rock or sediment. This configuration creates a situation where the water in the aquifer is under pressure. As a result, when a well is drilled into a confined aquifer, the water can rise above the top of the aquifer, and sometimes even flow to the surface without the need for pumping, a phenomenon known as artesian flow.

This pressure and stratification make confined aquifers significant in terms of water supply, as they can store substantial volumes of groundwater protected from immediate contamination by surface activities. The layers surrounding a confined aquifer, often composed of clay or other impermeable materials, serve as protective barriers that help maintain the water quality and prevent pollutants from entering the aquifer system.