Never seen this. Granted, I have only performed about 150 inspections but...
I have seen high efficiency furnaces / boilers with PVC exhaust but never a water heater with ABS... See photo. Any reason this is not acceptable? Also the entire set up is in a basement and the abs has about a 15' horizontal run before it daylights. It is fan assist exhaust but ABS?
(Please ignore extension chord...entirely different issue.)