Is there fossil water in the Sahara?

Yes, there are several large underground aquifers beneath the Sahara desert containing substantial amounts of fossil water. For instance, the Nubian Sandstone Aquifer System, located beneath parts of Egypt, Libya, Chad and Sudan, contains an estimated 150,000 cubic kilometers of water. This aquifer is considered to be a nonrenewable resource formed during prehistoric times when the climate was much wetter. Other notable fossil aquifers in the Sahara include the Great Artesian Basin in eastern Australia, the Ogallala Aquifer in North America, and the Guarani Aquifer in South America.