My 10 week old puppy just starting vomiting he has done this several times he seems fine otherwise. Should I worry? He is mastiff and I have heard some horror storys about "bloat" We are keeping a good eye on him but not sure what changes we should look for he did refuse water earlier. Whatever information you could give will be very much appreciated. Thank you!

At 10 weeks old bloat is not so much of a concern, a bigger concern would be things like parvo, obstruction, getting into something toxic, parasites.
Good that you want to know about bloat though, it would be a good thing for you to know about for future reference.

Is he up to date on his parvo/distemper vaccines and deworming?
Have you recently changed his food? Or given him people food?

Consider a trip to the vet soon if the vomiting is persisting, if accompanied by diarrhea get there even quicker.
You don't want to add dehydration to the list.

I'm posting you info on bloat for reference, but for the time being concern yourself with the other possibilities given his age.
Bloat (http://www.marvistavet.com/html/bloat.html)