The presence of pharmaceuticals and personal care products in the environment is a rapidly emerging international issue. A variety of drugs have been found in sewage effluents and surface waters in Europe, the United States, and Canada. This study examines the presence of selected pharmaceuticals (8 acidic drugs) and the antimicrobial substance, triclosan, in raw water and finished water of drinking water plants across southern Ontario. Twenty drinking water treatment plants that represented a variety of water sources and treatment process parameters were sampled. None of the raw or finished water samples taken from wells showed detectable levels of any of the acidic drugs or triclosan. River water samples downstream of sewage effluent outfalls showed the highest levels of contamination of the source water. Levels of naproxen and ibuprofen were elevated to levels as high as 176 and 150 ng/L, respectively, in raw water entering the treatment plants from a river source. Low levels of gemfibrozil (19.2 ng/L), diclofenac (15 ng/L), indomethacin (6 ng/L), and the antimicrobial triclosan (34 ng/L) could be also detected in raw water from river sources. Raw water taken from large lakes also had very low but detectable levels of several acidic drugs, suggesting that these chemicals are widespread in the environment. Although treatment systems are not designed to remove these specific types of substances, most of the acidic drugs were not detectable in finished waters. Naproxen and triclosan were detectable in finished water but were significantly reduced in concentration relative to the raw water. The concentration of ibuprofen was detectable in the finished water of almost all treatment plants that used surface water as a source. This work demonstrates the potential of Ontario source waters, particularly river water sources, to contain trace levels of selected pharmaceuticals and personal care products. There is a need to complete a more comprehensive assessment of these compounds in source waters and of the factors influencing their treatment and removal from finished drinking water.