You pay the overall utility bill for the building, but it expenses out the usage for each unit and then you invoice each tenant for their share.

If the bill is based on usage, I would bill the tenant back each month.

My only other thought is that maybe you could put in a couple of glamp sites that might comply with the land usage and generate a lot of additional income for the property. 

Just contacting them about your costs and asking them to open a claim on their insurance to cover them does not seem inappropriate to me. 

Not saying the S&P500 or the real estate is really worth or valued properly presently (I am even more convinced equities and property is grossly inflated and skewed inappropriately, but it is what it is). 

No physical difference (in terms of construction), no addressing difference, no land use difference, no zoning difference, no difference in how the County reports its usage, and nothing atypical for use in the neighborhood.Mine have just appraised as triplexes and been financed as such. 

Plus many seem to restrict your personal usage.

As others have said, if you didn't put any of this in writing, then you don't owe her anything.Unless you guys led her to believe she would be getting residual bonuses for every job you ever do for this client, it is absolutely inappropriate and crazy for her to expect you to be paying her out of follow up jobs.

I've been looking into companies like True Submeter and Metron meter for water which were mentioned on BP previously but they seem to be just meters connected on each device that measure all the water usage so thinking that could be an easier alternative? 

I think I would assume somewhere between $85-105/per unit for water costs per month - which could be more or less depending on your tenant's usage and the number of plumbing fixtures.