Warm up technique

I warm up by placing my penis and balls in a bowl of warm water. What I’m wondering about is whether it is safe or not to be putting my balls in the water? I don’t use extremely hot water so I’m not burning anything. But I’m worried that long term use of this could cause sterility. Someday I might actually want to have children (Right now I consider babies to be a form of STD). Are my fears irrational? I assume the warm water causes short term low sperm count, because heat kill’s sperm. Just wondering.