To investigate the occurrence of trace organic compounds (TrOCs) in waters throughout Arizona, 26 compounds (pharmaceuticals and personal care products (PPCPs), endocrine disrupting compounds (EDCs), and artificial sweetener) were analyzed in samples from surface waters, drinking water treatment plants (WTPs), wastewater treatment plants (WWTPs), and a groundwater recharge site during September 2007 to July 2009. Samples were analyzed using liquid chromatography/tandem mass spectrometry (LC/MS/MS). TrOCs were prevalent during this study, as they were found in 95% of the samples collected (n>100). The most frequently detected compounds in surface waters were oxybenzone, caffeine, and sucralose. The total concentration of TrOCs varied seasonally with the highest concentration detected during summer. For WTPs, the majority of TrOCs detected in surface water were also identified in WTP raw waters and sedimentation effluent. High TrOC concentrations were detected in raw wastewater, and certain compounds (e.g. oxybenzone, ibuprofen, DEET, etc.) exhibited an increasing trend during summer. WWTP processes were shown to remove 11 of 26 compounds with up to 98% efficiency. Sucralose and sulfamethoxazole were dominant compounds (>60%) in WWTP effluent. Pharmaceuticals were also present in the ground water system of the Phoenix water supply area (<5 ng/L). Overall, the top six compounds detected were a) by frequency: oxybenzone, caffeine, sucralose, DEET, sulfamethoxazole, and acetaminophen; and b) by concentration: oxybenzone, caffeine, sucralose, DEET, sulfamethoxazole, and dilantin. Results of this study demonstrate the occurrence of TrOCs in the Phoenix drinking water system. Other sources of TrOCs that might impact drinking water, such as lakes, WWTP recharging sites, and landfill sites, need to be investigated for overall water resource management in Arizona..