As one tale goes, the name also traces back to when workers building the railroad in Costa Rica were having trouble pronouncing words to their American and British bosses, and "water" came out like "guaro." Sounds more like a cute story than a historical fact, but, for what it's worth, color commentary is always good for small talk.
At 30% ABV, it is slightly less potent than vodka and, for the most part, tasteless. It is normally is mixed with sour or club for that reason, although taking it as a shooter is also acceptable amongst the younger crowd.
Why taste a tasteless liquor? Cause it's as the locals do! You'll find it behind every bar in Costa Rica, so give it a shot when you have the chance.