Water, water, everywhere,
Nor any drop to drink.
Samuel Taylor Coleridge, "The Rime of the Ancient Mariner"
Keeping his crew hydrated and non-mutinous was no easy task for a captain in the age of sail. The water, stored in casks, quickly became evil-looking and vile-tasting. Then, there was need to carry enough alcohol to keep crew in a tolerable state of sullenness.
When Europeans began distilling alcohol, it meant ships could carry the hard stuff instead the more bulky wine or beer. The Royal Navy switched from beer to rum and then grog. The French navy swapped wine to eau-de-vie
Turns out, this was a very big deal.
Grog, was 1 part rum mixed with 4 parts water AND LIME JUICE added for flavor. The daily ration 2.5 pints of grog versus the old ration of a gallon of beer.
And now, for the rest of the story:
The use of grog in place of beer played an unseen role during the eighteenth century in establishing British supremacy at sea. One of the main causes of death among sailors at the time was scurvy, a wasting disease that is now known to be caused by a lack of vitamin C. The best way to prevent it, discovered and forgotten many times during the eighteenth century, was to administer regular doses of lemon or lime juice. The inclusion of lemon or lime juice in grog, made compulsory in 1795, therefore reduced the incidence of scurvy dramatically. And since beer contains no vitamin C, switching from beer to grog made British crews far healthier overall. The opposite was true of their French counterparts, for whom the standard drink ration was not beer but three quarters of a liter of wine (the equivalent of a modern bottle). On long cruises, this ration was replaced by three- sixteenths of a liter of eau-de-vie. Since wine contains small amounts of vitamin C but eau-de-vie does not, the effect was to reduce the French navy's resistance to scurvy, just as the Royal Navy's resistance was increasing. The Royal Navy's unique ability to combat scurvy was said by one naval physician to have doubled its performance and contributed directly to Britain's eventual defeat of the French and Spanish fleets at Trafalgar in 1805.
Tom Standage, A History of the World in 6 Glasses