A solid phase extraction (SPE) method was developed and applied in conjunction with a previously reported liquid chromatography tandem mass spectrometry procedure in order to establish the presence of illicit drugs and abused pharmaceuticals in treated wastewater and surface water samples at the ng L-1 level. The procedure was applied in Dublin, Ireland, and rapidly expanding commuter towns in the surrounding counties. Cocaine was detected in 70% of the collected samples in the range of 25-489 ng L-1; its primary metabolite, benzoylecognine (BZE), was also detected, in the range of 22-290 ng L-1. Other substances detected included morphine, Tempazepam and the primary metabolite of methadone.