Where Does Water Come From?

If a five-year-old ever asks you this question, the answer is “rain”. That’s it. That will be enough. A five-year-old has very little interest in the evaporation/precipitation cycle, and even less interest in hydrogen and oxygen and that they’ve been around since the big bang. By the time you get to the strong and weak nuclear forces, they’re ignoring you and have already gone back to coloring or watching Looney Tunes. So save your breath. Water comes from rain.