sure they do, and love the idea of you,not them, struggling to adjust /repair them when they  break.  

For the tenants that will occupy the empty unit in the not too distant future I can make my own rental agreement, in particular, I plan to let them pay for the water as well, and I will set a reasonable security deposit.But for the tenants in the currently occupied unit:1) Would it be possible to write an addendum to the existing rental agreement to require the tenants to pay for their portion of the water bill?

Set expectations on paper for maintenance and repair process.

During a cost set study and expert will document and assess the value of every component of the property and produce a report  that itemizes the value by asset life. 

The professionals listed have additional training and ethic standards that set them a part, however it is important to conduct your own research and properly vet a few property managements before making your decision. 

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Where could you invest that money for a better return when you include adjustment for tax-free?

I am going through the pre licensing courses/ process now.My rough plan, as of current, is to begin flipping homes in desirable residential areas nearby and then move to flipping in the mountain/vacation setting.

(I set aside 20K from the rents after mortgages are paid, so basically I take in 68K a year, save 20K for vacancies, have 48K left over, etc.).Principal pay down is 67K a year.Appreciation is 500-800K a year in a good year.

However, if you're using a discount company that's allowing you as the owner to set the rent price, approve or deny apps, etc. then your issue could be one of many things.