Need fresh water line help '72 29'

[Airline]

Hi Airstream Lovers !
I am fixing some split copper fresh water pipes by replacing with pex.I am about to hook up the hot cold lines witch I think are going into the hot water heater.I am not sure witch line is Hot and Cold ( I did not mark them)
Can anyone tell me which of these two lines (with the new sharkbite fittings) is hot and which is cold ?

This is on a 1972 Ambassador 29' rear bathroom.

thanks !