Dry-mouth is a very common side effect for medications and it can even stick around after you stop taking the medications. It may be a personal bias due to medication use but I think it is 'need vs want' at that point. You may not suffer dehydration with dry mouth but it is uncomfortable.

I know that, but it’s by far the most common reason I hear for folks who carry water bottles everywhere, including office workers: they’re trying to get close to some very-high daily water intake recommendation.