Inmundicia translates to "filth" or "dirt," but it carries a stronger, more evocative connotation than just everyday grime. It suggests something morally or spiritually unclean, not just physically dirty.
In the song, Café Tacvba uses it metaphorically: "Agua para arrastrar la inmundicia / Que se ha acumulado sin querer." Here, water isn't just cleaning physical dirt; it's washing away accumulated emotional or spiritual impurities, making it a powerful and interesting word choice.
"Agua" uses water as a stand-in for everything the singer needs to heal and grow. Each verse asks water for a different kind of help: to clean old wounds, to wash away what has built up without anyone meaning for it to, and to feed a tree so it can eventually bear fruit.
The song moves from cleansing to renewal. By the end, the singer isn't just asking for water to fix what's broken. They're using it to quench a thirst that follows them and to raise a toast, because today they're back together with someone who matters.
It's a simple, hopeful image: water as the thing that clears away the past and makes new growth possible.