the stomach takes at least 3 hours to empty any meal. Water is the one which can empty quickest, that too takes 1 hour.
If you are a diabetic, there is an entity called diabetic gasteroperesis which can cause slow emptying of the stomach and vomiting
it can also be due to food poisoning
if it has occured once or twice or if it is associated with loose stools
you might need an upper GI endoscopy
kindly consult a medical gasteroenterologist