I think blowing in their face makes them hold their breath too doesn't it?
It's what they did at the baby swim class we went to. DS also would hold his breath when just out on a windy day.
My DS never liked his face to be wet, splashed or to be dunked or to have a little shower over his head, just hated all of that. I'm not even convinced that he would have got used to it, he just hated it, just his character I suspect. At his class they did the blow in the face followed by a shower of water on the head...and when they could manage that they did the blow and dunk. always counted down so the LO got used to when the blow and dunk would come (although my DS never did this).