Water bill never changed when the toilets leaked passed the flappers.You can talk to the water company and see if they can give you some analysis on usage. if the usage was steady, then it might be the flapper.

Mysterious Water Leak (estimate 200-300K Gallons a month):  Have had leak detection - NO LUCK, Sewer Camera Inspection (ensure water wasn't draining into sewer) - 95% confident it isnt, 2 Main Water Leaks repaired - stabilized water usage but still 200-300K gallons unaccounted for. 

It is sort of implied that an attempt is made to be fair.Submeters will prevent tenants from complaining about other tenants' water usage which is worth something.  

I have found some with rs485 or straight mechanical meters etc. but I'm looking to submeter the attached apartment at my SFH and be able to access usage data over my LAN to keep from physically reading the meter every month. 

Make sure you have  in your agreement that they do so at their own risk and that they hold you harmless  for their usage. 

There is no reason for a landlord to be carrying any costs on a property if those items do not have a fixed monthly fee.If the service has a fixed cost, flat rate charge, the landlord can build it into the rent however if it is based on tenant usage the monthly cost should be billed to the tenant by the landlord separate from the rent monthly.

This is the first year doing this so we will see how great this option works, but seeing as we rent it all inclusive, I would rather spend a bit on the upfront cost for the sensors and use our gas furnace, then spend the upfront cost for electric heaters to supplement and pay for the electricity usage as well.  

While some drugs are now considered legal, I would not want visitors/potential tenants to perceive my properties as places where we advocate drug usage or that it's okay to leave personal items wherever you leave them.

These bills should be monitored for usage rates compared to historical data.

They also bill you residents for water usage each month based on local rates.