If the faucet just has a single water inlet, then to get warm water you use a simple mixing valve like this one:
I'm helping my brother in law install a touchless faucet. The directions say to use a T w/backflow preventers to hook up the hot and cold into the unit.I have not been able to find such part even at my local plumbing store. Is it really necessary to have backflow preventers with the T? If so does anyone know where I might find one. Google mostly gives me much bigger backflow preventers than I need or could possible use under a sink.