If so, you are far better off leaving them on, assuming you're not planning to replace the plumbing already. 

I also ended up having to replace all the plumbing into the unit because of the care provided by previous owners. 

. $4k per bathroom, $10k for the kitchen (including SS used appliances), $1k per window, $3k interior paint, $5k for wood laminate flooring, $7k plumbing update, $4k electrical update, $3k asphalt driveway, $3k furnaceMy guesses are based on rehabs at three properties in the last four years.  

Is anyone aware of any similar acts, rules, regulations, laws, etc., in states of Oregon, Nevada or California?

The term is also used to refer to the bank regulation which governs these activities.

They're regulated and have liability.  

Regarding residential work on existing structures, only a licensed Contractor is legally permitted to enter into an agreement with a licensed Subcontractor (save for those who hold trade specific licenses for electrical, plumbing and HVACR).  

There are usually laws regarding minimum standards for plumbing, air flow, and heating, fire safety standards, etc that are affected by the number of unrelated people renting part of the same dwelling.

My dad then hired him to finish the basement w/ carpet, drop ceiling, build a bathroom (plumbing rough-in was existing) and bedroom.  

You might also need to check on regulations, depending on the areas.