A U.S.-wide occurrence survey conducted as part of the Unregulated Contaminant Monitoring Rule 2 found that N-nitrosodimethylamine (NDMA) was present in 34% of chloraminated drinking water samples but was the most prevalent of the six N-nitrosamines evaluated using U.S. Environmental Protection Agency (EPA) Method 521. If the U.S. EPA considers limiting exposures to N-nitrosamines as a group, a critical question is whether NDMA is the most prevalent N-nitrosamine or whether significant concentrations occur for N-nitrosamines other than those captured by EPA Method 521. A total N-nitrosamine assay was developed and applied to 36 drinking water plant effluents or distribution system samples from 11 utilities, including 9 utilities that practiced chloramination for secondary disinfection. Concurrent application of EPA Method 521 indicated that NDMA was the most prevalent of the Method 521 N-nitrosamines yet accounted for ∼5% of the total N-nitrosamine pool on a median basis. Among eight plant influent waters, NDMA was detected once, while total N-nitrosamines were detected in five samples, suggesting the importance of source water protection. Similar to NDMA, total N-nitrosamine concentrations in source waters increased after chloramination. Chloramines were applied to organic precursors serving as models for pristine natural organic matter, algal exudate, wastewater effluent, and polyDADMAC quaternary amine-based coagulation polymers. While high yields of NDMA were restricted to the wastewater effluent and polyDADMAC, high yields of total N-nitrosamines were observed from the algal exudate, the wastewater effluent, and polyDADMAC. The results suggest that N-nitrosamines as a class may be more prevalent than suggested by occurrence surveys conducted using EPA Method 521.