Minimal temperature setting for hot water heater to prevent legionella
OSHA recommends  a water heater temperature of 140 Fahrenheit  (60 degrees Celsius)  to prevent legionella growth.
The CDC  has information that is helpful.
As a landlord you will want to prevent scalding and legal issues associated with scalding,  so  anti-scald devises would be recommended.
Doing your own research would be the proper way to educate yourself as to  guidelines and pertinent info  to address your concerns.
Also, ask your local health Dept for any public resources/info available in your area.