It makes no difference at all. To sterilize your hands you would need to wash them with water at around 115 degrees C at 1.2 atmospheres of pressure for over 30 minutes – that's obviously not going to happen. The bacteria that normally reside on your skin can easily tolerate tap water, no matter whether the faucet is set to maximum hot or maximum cold, or just average. Even if the temperature of the water could appreciably slow down bacterial growth (which it can't), once you've washed your hands your skin temperature goes back to as it was before the washing in a minute or so.