If one makes a נדר not to eat and he drinks less then an ounce, is he חייב
A.) Is drinking included in his vow at all
B.) Is drinking so little considered breaking his vow
The terminology that you used sounds more like a shevuah, because a neder would be that “food is forbidden to me”, but if he says that he won’t eat, it is a shevuah. If one swears not to eat it includes drinking, and he is forbidden to eat even a drop, even less than an ounce He will not get malkos however unless he eats a kzayis
Avodah Zara 22b, Y:D 238-1,2.