Rather than being such a lazy Pollyanna and posting a question to a forum full of ignorant bombastic self-important morons (like me, for example) and hoping to get accurate and concise information, I suggest you google (or bing?) the question and look for information on presumably "legitimate" sites, like these for instance:

http://www.mayoclinic.com/health/caf...drinks/AN01661
http://answers.webmd.com/answers/116...ine-a-diuretic
http://www.ncbi.nlm.nih.gov/pubmed/19774754
http://www.nytimes.com/2008/03/04/he...on/04real.html
http://www.livestrong.com/article/29...s-of-caffeine/

("legitimate" Decide for yourself the relative legitimacy of the above sites...)