My DS does it too. He's much braver than DD is in the water. DS and DD bathe together, and I will leave the room for a few mins at a time to get stuff organised. I keep my ears open for them talking and splashing and I'm in and out every few mins to check on them. I'm never out for more than about 3ish mins withough looking in on them. I like that DS is so confident in the water. I feel that if he ever went under he would manage to get up on his own, where as with DD I think she would panic and have trouble in the water alone. Of course I hope that never happens!!