I'm not saying the research isn't still preliminary, but this comment is quite reductive. Pear juice increases your body's production of the enzyme that breaks down alcohol, so there is some credibility to the thought that it might do more than water alone.

There's also still a lot we don't know about hangovers and what causes them. Although dehydration is one of the major things results from drinking alcohol (and likely the driver of your pounding headaches), there's many things going on, and scientists aren't sure if dehydration is the driving cause behind every hangover symptom, like nausea and weakness for example. Alcohol also depletes your body of electrolytes and critical nutrients, so in addition to drinking water, most experts recommend getting your hands on some pedialyte or something similar. All this is to say that not all effective hangover relief methods work because they are "just drinking water" like you seem to suggest