I was always taught that to correctly wash your hands you need at least warm water (don't know the specific degree) and soap and rub for the amount of time it takes to sing "Frere Jacques".
I understand about the fear of scalding, I was once in a local restaurant whose hot water was so hot I felt the need to talk to the manager about it. but that was an exception.
To me, my hands just don't feel clean unless I have warm water. Doesn't have to be hot, but at least a little warm will satisfy me.
And I am the daughter and sister of nurses.