I know that the OP is referring specifically to Water and Sewer.
When I have visited Myrtle Beach, I have seen all of those various blue and white City of Myrtle Beach vehicles driving around and wondered what radio system they use. Back when Myrtle Beach operated their own trunked radio system, I think most city departments used it. But it was decommissioned several years ago. Those departments are not on the Horry County trunked radio system that I can tell, nor are they on Palmetto 800. Once I started paying attention, it appeared to me that most city vehicles don't have any LMR antennas on them at all, other than City emergency services vehicles. It makes me suspect that most MB city departments probably use mobile phones and commercial wireless services for data.
If anyone knows differently, please chime in.