I know that the amoralist Joel Marks advocates your position. But I agree with Russel Blackford in The Mystery of Moral Authority that it is impractical not to use 'ought' and 'should' in a conversation. More often than not, we use them non-morally and to recommend a course of action to achieve a goal. To simply state "You will die if you don't drink water" is to state a fact, not to make a recommendation; saying "you should/ought to drink water" better conveys the intention.

I am certain that there are many other reasons to prefer using ought/should in conversations. One of these is that we can say "you ought to do x" while the context of the conversation makes it implicitly understood why you should do it. In this sense, all you have to do is say "You should drink more water" rather than say the full sentence "You should drink more water if you want to stay hydrated and healthy."

In the sense I have brought it up in, ought or should (as well terms like good, bad, fair, et cetera) are better understood as part of a social technology to ease our communication. This is the point that the aforementioned Russell Blackford makes in regard to moral language.