This lecture extends previous discussion on various types of aquifers and related geological formations. Aquifers are classified into confined and unconfined types, with unconfined aquifers receiving water directly from the surface. Aquitards are low permeability units that can store and slowly transmit groundwater, while aquicludes are porous but impermeable formations that do not transmit water. Leaky aquifers, also known as leaky confined aquifers, are bounded by semi-pervious layers, allowing water to gain or lose through these layers. Artesian aquifers have a piezometric surface above ground level, causing water to flow out automatically when a well is drilled.