Doses of caffeine equivalent to the amount normally found in standard servings of tea, coffee and carbonated soft drinks appear to have no diuretic action.  However, acute ingestion of caffeine in large doses (at least 250–300 mg, equivalent to the amount found in 2–3 cups of coffee or 5–8 cups of tea) results in a short-term stimulation of urine output in individuals who have been deprived of caffeine for a period of days or weeks.  This increase is due to both a diuresis (increase in water excretion) and a natriuresis (increase in saline excretion); it is mediated via proximal tubular adenosine receptor blockade.  The acute increase in urinary output may increase the risk of dehydration . However, chronic users of caffeine develop a tolerance to this effect, and experience no increase in urinary output.  
Personally, I wouldn’t bother buying these watches new. I would buy them pre-owned from a reputable watch dealer, and then send them to Lange/JLC for a service. Lange, for instance, uses a laser metal deposition technique when polishing the watches, which means that the case of a serviced timepiece won’t loose any weight, and ends up looking just like a brand-new watch. Even after factoring in the servicing costs (which in the case of Lange and JLC are quite decent), buying these watches pre-owned will bring you considerable savings — €30,000 for the Lange, and around €20,000 – €25,000 for the JLC.