Is she actually vomiting the water up or is it just falling out of her mouth.... there is a difference ... some large
breed dogs (Mastiffs, Danes, Rotts etc.) will have water fall out and this can be normal.... but if the dog is actually throwing up water and she has never done this before.... she needs to be seen by a vet ASAP because, I would seriously suspect some type of internal blockage ... numerous times I have read about people whose dogs all of a sudden display similar behavior to this ... they decide to wait it out instead of bringing their pet to the vet and then will go about their regular day to come home to find their dog has passed on in a not so great way .... In no way is it ever normal for a dog to be puking after they drink water, the dog should be seen by a vet.
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~Ignorance can be cured with education~
Mom to:
A little girl (6) and a little boy (4), and 2 dogs

Leo and

Gunner
Proud Coastie Sister!! 
My brother is in Virginia at FT school !!
RIP Ed

October 2000-November 2007