Seems like a good time to make it right. In the first place, PVC is not legal for indoor use. Perhaps it's CPVC? Anyway, it's Mickey Moused for sure. What I'd do is convert to 1/2" copper from the water heater to a convienent spot below the DW. There I'd put a valve and an adapter to a flex hose to run through the floor to the DW. I'm not sure what size it takes, likely 1/2", but maybe as small as 3/8". You definitely need a cutoff valve between the water heater and the DW in a place that can be accessed. I'd use a 1/2" ball valve.