The answer is E.

The sentence acknowledges that discussions about water shortages often use apocalyptic rhetoric - which can be seen as exaggerated or overly dramatic - even though the essential message about water scarcity is valid.

A. abstract: Abstract language is theoretical and not concrete. In the context of impending water shortages, this term doesn't align with the idea of conveying a clear and urgent message.
B. complacent: Complacent language implies a sense of self-satisfaction or unconcern. In the context of discussions about water shortages, it doesn't convey the urgency or seriousness of the situation.
C. ambiguous: Ambiguous language is unclear and open to interpretation. In the context of impending water shortages, this term doesn't align with the idea of conveying a clear and straightforward message.
D. unfamiliar: Unfamiliar language suggests something not widely known or recognized. In the context of impending water shortages, the language used may indeed be familiar, so this term doesn't fit the context.
E. overblown: Overblown language is exaggerated or excessive. This term accurately conveys the idea that discussions about water shortages are often characterized by exaggerated or overly dramatic rhetoric, while the core message about water scarcity remains valid.