Typically they will review usage or it comes up during permit phase.One thing you can try to do but most likely not be successful is to speak with other neighbors and see if by increasing the size even bigger they will pitch In for some costs in case they want to do the same later on.

We also charge for early check in/late check out, pets, dock usage where available, and pool heat where available. 

Liability Waivers: Do you recommend having guests sign a liability waiver related to pool usage?

The water company will actually print you the water usage amount and you can calculate usage from there, often times without the owners permission as it is just numbers.

You could just produce a lease with CAM charges and bill according to overall usage divided by four Or charge more for rent to cover water and sewer fees.

Make sure you check out STR permits in your area because the Nashville market is restricting usage and permit access all the time.

I'm considering putting dishwashers and Washer/dryer in all units but have concerns about excessive water usage.

I don't know if one of the tenants is abusing the water usage, or can there be a major water problem with the city? 

For normal usage, a tenant should expect it to go down. 

Even if the circuit does run to one or two outlets in addition to the lighting, you're OK as long as the tenant doesn't connect a max-usage, long-service appliance to the circuit, most commonly a space heater.Put the first electrician in charge.