The worldwide pressure on fresh water resources and bleak predictions for reducing water availability associated with climate change in arid and semi arid zones, has led to intensive research for alternative water supply, including utilization of unconventional resources such as saline waters and waste waters. Considerable technical progress has been achieved in desalination, dominated by Reverse Osmosis (RO) desalination. We previously have investigated the geochemistry and isotope (oxygen, hydrogen, boron lithium) composition of water associated with RO desalination (paper in Environmental Science and Technology ) where we showed that man-made drinking water has a different composition relative to natural meteoric water. Following, we have investigated the geochemistry of RO desalination of saline groundwater from the Outer Banks of North Carolina (paper in Hydrogeology Journal ). We showed that relatively high levels of boron and arsenic (in the form of AsIII) in the saline groundwater require additional treatment, as the typical RO desalination membrane is not capable to remove these elements. The groundwater geochemistry, therefore, has an important impact on the ability and economics of RO desalination. Given that the combination of population growth and water scarcity in arid zones is expected to enforce massive production of desalinated water, mostly using RO technology, we anticipate that the inevitable release of man-made water will modify the natural chemical composition of the hydrosphere during the next decades.