I will make this short: A while back (late last year) my water needed to turned off. So the water district had to feed my house & the house to my south (shared main) from the house on north side. REVERSE FLOW.
Well that does $900.00 damage to my water softener. Letter sent for damages. Will see what happens. The reason it took so long to discover the problem is my salt tank is big and I only check every 6 months.