I agree you should use one, and an adjustable one at that if you don't know what the water pressure is where you are hooked up. I know my pressure at my house is minimum 30 and max 50, that's my pressure switch on my well. If I were hooked up in town or an RV park, for sure I would have a regulator and gage. In my Girard owners manual, page 12, #1. Says, "The RV's cold water system deriving its water input from a pressurized (45 psi or greater) source as a shore connection....), Page 3, Water Operating Pressure 125 PSI MAX. Page 5 says For proper operation this water heater requires a minimum water flow of .7 gallon per minute for each Hot Water faucet it supplies. I think if you have all these things like the book says, the water heater should work fine. The water lines in the newer RVs are PEX and it will easily stand 65 or 70 PSI. I have one of the Camco regulators that has a yellow arc that say low, a green arc, and a red arc that says high, no numbers so I don't really know what they are calling low or high so a I am going to get an adjustable one with a gage and set it for about 55 psi and see how well it works, I am betting it's going to work just fine.