Knowledge is power.
I think the reason for serving water before tea could also be for the same reason. To keep you hydrated, to avoid acidity or gastric problem. Also water intake improves the metabolism so water might be given so that there is balance and metabolism is not disrupted after having tea.
I won't comment on the scientific part but would like to clarify that it is a normal routine to offer water to a guest before anything else. I don't think it is specific to any hotel and we need to understand that it is done even when someone visits our home. It is a part of our ethics and good manners.
“There is only one good, knowledge, and one evil, ignorance." -Socrates
When you make a commitment, you create hope. When you keep a commitment you create trust! ~ John C. Maxwell
As far as my knowledge goes, it is not good to water before drinking tea. We should give some minimum gap between these two. The water we will take will be at room temperature or even less but tea will be at a higher temperature. This difference in temperatures is not good for the body. Many doctors suggest this.
if we drink water sufficiently in a day, we need not take water separately before taking tea. But we should see that we will have a minimum intake of water.