The US based Food and Nutrition Board of the Institute of Medicine in its February 2004 report on «Dietary Reference Intakes for Water, Potassium, Sodium, Chloride and Sulfate» states, ``... caffeinated beverages appear to contribute to the daily total water intake similar to that contributed by Non-Caffeinated beverages.» (australianbeverages.org)
... Hence, unless additional evidence becomes available indicating cumulative total water deficits in individuals with habitual intakes of significant amounts of caffeine, caffeinated beverages appear to contribute to the daily total water intake similar to that contributed by noncaffeinated beverages.» (kellymom.com)
Results: In 2005 — 2006, American adults reported consuming 3.18 L of total water within the previous 24 h (in 1999 — 2004, estimated total water intake was 3.35 L), with plain water and beverages contributing 33 % and 48 % of the total, respectively. (academic.oup.com)