Seawater infiltrates the water table where it comes into contact with fresh water, but because it is heavier, seawater usually lies below the fresh-water layer.

However, when fresh water in coastal regions is drawn to the surface via drilling, and its level drops, so too does its resistance to the infiltration of seawater.

Moreover, drawing up large volumes of water at one point can create a «cone» of seawater underneath the drill, drawing it up to the surface.

As more and more seawater infiltrates the water table, the quality of the fresh water changes, becoming brackish and eventually salty.