Pharmaceuticals and Endocrine Disrupting Compounds: Implications for Ground Water Replenishment with Recycled Water by Mark J. Benotti 1 and Shane A. Snyder 2 1 Applied Research and Development Center, Southern Nevada Water Authority, P.O. Box 99954, Las Vegas, NV 89193-9954; (702) 856-3684; fax: (702) 856-3647; mark.benotti@snwa.com 2 Applied Research and Development Center, Southern Nevada Water Authority, P.O. Box 99954, Las Vegas, NV 89193-9954; (702) 856-3684; fax: (702) 856-3647; shane.snyder@snwa.com Increasing human population has put unsustainable demands on fresh water resources, particularly in arid areas of the world. One piece of evidence is the extensive ground water depletion that has occurred in areas due to the combination of population growth and urbanization. Increased water withdrawal leads to ground water deple- tion when withdrawal rates outpace replenishment rates. Ground water depletion is exacerbated by urbanization, as paved surfaces divert water that would otherwise percolate into aquifers. Ground water replenishment with recycled water is an important and necessary practice and offers several beneficial outcomes. First and foremost, its use helps mitigate ground water depletion and the adverse effects that can accompany it, such as land subsidence and sea water intrusion in coastal environments. Second, it maintains water within the watershed or basin (i.e., the water is not lost to surface water outflow from the water- shed or discharge to the ocean). Third, it can provide a significant cost savings over alternative water sources. There are, however, concerns over the quality of the recycled water used in ground water replenishment sys- tems. Waste water–borne pathogens, nutrients, and bio- logical oxygen demand are the most significant concerns for waste water utilities, as these parameters are most commonly monitored in receiving waters. Recently, these trace-level waste water – derived organic contaminants have NGWA.org Vol. 47, No. 4–GROUND WATER–July-August 2009 499