The different types of groundwater sources can be classified as confined or unconfined aquifers. Confined aquifers are located beneath impermeable layers, receiving water from distant sources. Unconfined aquifers are close to the surface and receive water primarily from surface infiltration. Other types of groundwater sources include springs, which occur where groundwater naturally emerges at the Earth's surface, and artesian wells, which tap into confined aquifers and produce groundwater under pressure. Additionally, there are also regional and local aquifers, which describe the scale and extent of the groundwater source in a particular area.«Groundwater contamination potential from stormwater infiltration practices »