While some people might consider a beer or two (or more) to be "performance enhancing,"  apparently World Sailing and WADA do not.  (A search for "alcohol" and "ethanol" in those linked documents produced no results.)

Your local law enforcement agencies may have another opinion.  (In most states within the United States, operating a boat with a blood alcohol level of 0.08% will earn you a night in jail.)

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In ARG, operating a boat with a blood alcohol level of 0.05% will earn you a night in jail.
......but, all over the world, one thing is the law, and other is reality

 

Alcohol may not be a prohibited substance, but plenty of other commonly taken medications are.  Technically, any diabetic who takes insulin is breaking rule 5, unless he or she gets special permission from the World Anti-Doping Agency. Women who have had estrogen-positive breast cancer take anastozole, a prohibited substance, every day, and if they're not Olympic contenders I doubt very much if they have applied for permission to use the drug.  And so it goes on -- remember, all those drugs on the list were developed by pharmaceutical companies to treat illnesses.  

This whole thing (as well as RRS 6, Betting and Anti-Corruption, which we only wish our sport was important enough to worry about) is driven by the Olympics.  The IOC requires that each Olympic sport apply these rules to everybody in the sport, even those who have no connection with the Olympics and never will.  Of course, RRS 5 is not enforced at any level of sailing other than Olympic or pre-Olympic events, so we end up being hypocrites.  

The Olympics are a big motivator for young, hot sailors, so they do provide some benefit to our sport.  But how many US sailors are motivated by the Olympics?  50?  100?  And tying the sport to the Olympics causes harm, as in the case of RRS 5 and 6 and the huge amount of effort dedicated to the selection of equipment, the venues of Olympic events, the running of events dedicated to Olympic Classes, providing coaching, and so forth.  There should be an open discussion about whether the benefits out-weigh the drawbacks, but, alas, World Sailing is almost completely funded by the IOC, so that discussion will likely never occur.  Of course, US Sailing could back out of the Olympics, but then World Sailing would no doubt accredit some rival organization to the the MNA for the US, and nobody wants that.  So we live with rule 5 and the hypocracy.

 Alcohol used to be in the prohibited list for some sports only (Aeronautics, Archery, Automobile, Karate, Motor Cycling, Power boats....). But, it was removed completely from the list on 2018.