Abstract Background Soft tissue or skin infections due to nontuberculous mycobacteria (NTM) have been reported frequently and are mostly associated with trauma or cosmetic interventions like plastic surgery. However, infection with NTM as a result of a dental procedure have rarely been described and the lack of clinical suspicion and a clear clinical manifestation makes diagnosis challenging. Case presentation We report on three patients with a facial cutaneous sinus tract of dental origin, due to an infection with respectively Mycobacterium fortuitum, M. abscessus and M. peregrinum. The infection source was the dental unit waterlines (DUWLs), which were colonized with NTM. Conclusions Water of the DUWL can pose a health risk. This report emphasizes the need for quality control and certification of water flowing through DUWLs, including the absence of NTM. Our report also shows the need for a rapid recognition of NTM infections and accurate laboratory diagnosis in order to avoid long-term ineffective antibiotic treatment.