From the Center for Disease Control’s “Show Me the Science — How to Wash Your Hands”:
Wet your hands with clean, running water (warm or cold), turn off
the tap, and apply soap.
Why? Because hands could become recontaminated if placed in a
basin of standing water that has been contaminated through
previous use, clean running water should be used. However, washing
with non-potable water when necessary may still improve health.
The temperature of the water does not appear to affect microbe
removal; however, warmer water may cause more skin irritation and
is more environmentally costly.
Turning off the faucet after wetting hands saves water, and there
are few data to prove whether significant numbers of germs are
transferred between hands and the faucet.
I’ve always washed my hands with water as hot as I can take it. (Well, that’s not quite true — but when I’ve used cold or cool water because the hot water was taking too long, I’ve felt guilty about it.) It’s just mind-blowing to me that the recipe is just soap and clean water of any temperature.