The main objectives of this study were to develop a sensitive method to analyze nine nitrosamines in drinking water and to evaluate their occurrence in raw water and treated water samples from public water systems. About 600 samples (raw water and treated water) equally distributed across the 100 French departments, were collected from October 2011 to May 2012. This sampling, represents about 20% of the national water supply flow. In raw water samples, no molecule was detected for 95% of the samples. Only N-nitrosodimethylamine (NDMA) and N-nitrosomorpholine (NMOR) were identified. In treated water, among the nine nitrosamines analysed, only NDMA, NMOR and N-nitrosodiethylamine (NDEA) were quantified. This campaign also revealed concentrations higher than 1000 ng/l for NMOR in raw and treated water of a municipality. Further investigations highlighted concentrations of NMOR up to 3000 ng/L in close water supplies and up to 17500 ng/L in the nearby river downstream to an industrial site. This pharmaceutical site uses annually several thousand tons of morpholine in its process of manufacturing, and produces unintentionally NMOR in its wastewater treatment plant, due to acidic conditions.