A wet site is an event where alcohol is permitted, although all SCAdians expect a certain level of behaviour at even wet sites. Getting a little tipsy is generally accepted at wet SCA events, provided one does not become sloppy or offensive.
Some events are labelled with phrases such as "discreetly wet". In these cases some extra rules will apply (ask the event organiser for the specifics), generally due to restrictions on site hire. Alcohol consumption should be discrete ie bottles hidden and inbibers behaviour not suficiently drunken to attract attention. In some cases bottles should be removed from the site, so as to leave no evidence of drinking (generally youth camps, where next weeks minors may not appreciate that the last group were responsible adults).