Recently we have had to open fire hydrants to flush water out of the system. The explanation we got is that the chemicals they use to treat it eventually cause it to got out of safe spec.
Hydrants also need to be flushed and checked periodically to get rid of sediment and debris in the pipe lines and to make sure that there is enough pressure at the hydrant to fight fires if needed.
Pipe repairs in the system will also require that the lines be flushed to get rid of dirt or debris that enters the pipes during repair.
I was about to note that they do this all the time...but we live no more than 50 miles from each other...
Every few weeks, there’s always a giant puddle on the roads...