Most Japanese drink tea (not always green tea), instead of water, during meals. In my case, alcoholic beverages more commonly come with dinner, though.
Recently, my 12-year-old daughter has started to drink water at the table. She said that water is good because it keeps her teeth whiter. She added that avoiding drinking tea is common sense among her friends. As expected, my two sons do not accept the concept.
I am not sure if there is evidence to show the association of drinking water with darkening teeth, although the relationship is intuitive. If so, a red wine would be more tightly connected to change in color of teeth, because my teeth look dark after having dinner with red wine.
I may know the answer 10years later, when I compare the color of teeth between my three children.