Coca Cola contains relatively little caffeine by fluid volume compared to, say, coffee. But more importantly, it's well documented that regular users of caffein

Coca Cola contains relatively little caffeine by fluid volume compared to, say, coffee. But more importantly, it's well documented that regular users of caffeine build up tolerance to its diuretic effects. From the Wikipedia page on caffeine: "Most people who consume caffeine, however, ingest it daily. Regular users of caffeine have been shown to develop a strong tolerance to the diuretic effect,[34] and studies have generally failed to support the notion that ordinary consumption of caffeinated beverages contributes significantly to dehydration, even in athletes.[35][36][37]" Here are the references: [34] ^ a b c Maughan RJ, Griffin J (December 2003). "Caffeine ingestion and fluid balance: a review". J Hum Nutr Diet 16 (6): 411–20. doi:10.1046/j.1365-277X.2003.00477.x. PMID 19774754. [35] ^ O'connor, Anahad (2008-03-04). "Really? The claim: caffeine causes dehydration". The New York Times. Retrieved 2009-08-03. [36] ^ Armstrong LE, Casa DJ, Maresh CM, Ganio MS (July 2007). "Caffeine, fluid-electrolyte balance, temperature regulation, and exercise-heat tolerance". Exerc Sport Sci Rev 35 (3): 135–40. doi:10.1097/jes.0b013e3180a02cc1. PMID 17620932. [37] ^ Armstrong LE, Pumerantz AC, Roti MW, Judelson DA, Watson G, Dias JC, Sokmen B, Casa DJ, Maresh CM, Lieberman H, Kellogg M (June 2005). "Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption". Int J Sport Nutr Exerc Metab 15 (3): 252–65. PMID 16131696.