The map above is a part of a recently released world map that shows, in blue, the presence of the underground water. I've cropped the part that shows the Middle East and North Africa. The part that are shaded in red show aquifers that have been infiltrated by seawater, i.e. where the water salinity is high. This may be for different reasons, although generally (and specifically in Egypt's case) it is because overuse of underground freshwater is drawing in seawater.
Link to full world map.
Link to World-wide Hydrogeological Mapping and Assessment Programme (WHYMAP) site.