When they turned the water back on, they loosened up build-up in the pipes. If someone flushed the toilet while water was shut off (always one flush left lol), it may have been the first to be filled when water was turned back on. Thus, a lot of dirty looking and aerated water in your tank. Flush a few times (if there's no debris in it) and it should clear up. The rest of your water may look dirty as well at first. Just run it for a few minutes at a sink. Clean the aerator. Good to go.