Then wherever the water is getting discharged off of the roof, that what water is getting at least 4-5 foot away from the structure before it is left to drain with gravity away from the property. 

Water meter-water company.  

What if you turn on water and it goes everywhere.

Water overflowing the sink, seems more plausible than some missing caulk.  

And I will state different jurisdictions have different rules, processes, expectations, etc.In my area you are required to have a permit to swap a water heater.

The meters are read electronically with 3g and you get great reporting in their water scope platform.

City water with one main at the street and how will they bill. 

I used to live in the city and the taxes and water bills are nightmares.

Don't forget to change all your faucet aerators and shower heads to low flow it makes a huge difference as well as far as water usage and saving HOT water. 

I would also look at the availability of public water and public sewer, if not at the site how far away are those services.