How to check how much water my dishwasher is using?
This is NOT intended use

It's way too much water for any intended use. 

To give you an idea, the last time I saw a $700 bill, it was from a toilet at a rarely-used facility, which had a stuck float. The valve was wide open 24x7 for 2 months.  That's the kind of flow we're talking about.   

For a dishwasher to have that much flow, it would have to be waterfalling 24x7, running its little pump to death.   So that's not likely, due to the dishwasher's need to pump its wastewater up. 

It is absolutely impossible for a dishwasher to overuse that much water during the hour or so a day it is in-use. 

Outside of toilets, you'd know about any appliances leaking that much water, because their usage is obvious. You'd notice if a shower, tub or sink was running full-on.  

The only things that remain are: 


A pipe break somewhere unnoticed, like in lines under a slab, soaking into the dirt. Pay close attention to any blooms of vegetation, lush spots in the lawn, etc.  
A tenant who has insanely or maliciously thrown water valves wide open, e.g. a vacating tenant on their way out the door.  Or a hardware failure in a vacant apartment.  So do a walkthrough on any vacant apartments.