That’s… Actually probably exactly how Star Trek would handle modern Earth. Part of the prime directive is that any species that gets contacted by the Federation has to achieve a certain level of technological and societal advancement first, and we’re close, but I’m pretty sure we’d get put on the “check back in a century” list.
So, if they’re nice aliens and they just watch us for a while and leave, maybe our first contact just got waitlisted?
It’s pretty easy to break water down, but it’s also super easy to make it - just burn anything organic.
Usually you can’t see the water being formed, but there’s actually a really common example: car exhausts on a cold day. If you notice a bit of water dripping out of the tailpipe of the car in front of you at a red light, that’s actually the moisture in the exhaust fumes condensing on the cold tailpipe.