Pharmaceutically active compounds (PACs) are widely used around the world to maintain human and animal health. There is growing concern that these compounds pass through sewage‐treatment plants and enter the environment for potential harmful effects on living things. In this study, the occurrence of nine PACs (acetaminophen, caffeine, carbamazepine, codeine, methyltestosterone, metoprolol, propranolol, stanozolol, and testosterone) in hospital wastewater, sewage wastewater, raw water used for drinking water, and treated water was studied in three sampling events representing different flow conditions, i.e., December, April, and June 2010–2011. Most of the target compounds were detected in both hospital and sewage wastewater samples rather than in drinking water samples. The most frequently detected compounds in the samples were acetaminophen and caffeine with increased concentrations of up to 160 µg/L in sewage wastewater, while their concentrations were significantly lower in raw water. Generally, a seasonal variation of the test compounds in the samples was significant. All drugs were detected in higher levels during winter as drug use for diseases might increase through this season and a faster degradation and removal might occur during summer. The results showed that water had been polluted with these substances, and although purified by water treatment, reached humans via drinking water.