USUALLY a water department can tell you how long the water meter has been running constantly. 

Hot tubs pay for themselves.  

I’m curious to get some data on what people are spending on water/sewage each month on their duplexes….As the owner, water/sewage are the utilities I expect to pay myself.

Quote from @Joel Oh: Quote from @JD Martin: I have a salt water hot tub at my personal home.

The issue with watering your foundation is that you have to do it always, every year without a break in order to achieve the desired effect.

For those that have 5+ year old water softeners.

I thought that we would be able to charge more rent for the units which included heat and hot water. 

If the water bill is $100 a month, increase the price by 20% (or whatever you decide is fair) to compensate you for the time required to split and bill and to cover additional use when tenants squander the utility.

People want to be on the water not near it.

Now you can advertise it as having a sump pump to prevent future water damage when you can sell.