There are about 25 million people who are Muslim, or 97% of the total population. Data for Saudi Arabia comes primarily from general population surveys, which are less reliable than censuses or large-scale demographic and health surveys for estimating minority-majority ratios.
Until the 1980s, Saudi Arabia had lakes at Layla Aflaj and deep waterholes at Al-Kharj, fed by huge underground aquifers, formed in prehistoric times and non-renewable. Al Kharj was a valuable source of drinking water in an barren terrain. In recent years, these aquifer have been drawn upon heavily, both for agricultural and domestic purposes, and no fresh water remain in the lakes or pits.