So... By that logic, sleeping must also be bad for ones teeth. Unless of course they talk in their sleep.
-Stoic Joker
It would explain the morning breath phenomenon.
Who is most likely to need-a-drink? Some one waiting in line alone? Or someone giving a speech??
-Stoic Joker
Don't confuse dry mouth with dry throat. One doesn't necessarily have anything to do with the other.
I don't think this dentist's advice could hurt you if he's wrong and could only help if he is right. I do know the habit a lot of people have of guzzling a lot of sugar loaded soft drinks, tea, coffee, etc while working can't be good for your teeth, so just the act of replacing that with water could do a lot of people's teeth a lot of good. And don't forget that even if you use a sugar-free sweetener in your tea or coffee, if you are adding milk, it still has sugar in it.