Yeah, but like an umbrella made by something like Drexler's nanotechology.

How about something more ... Realistic

https://www.thebrighterside.news/post/mits-high-tech-hydroge...

That's the opposite of a tree, which turns drinking water into nothing

"Water harvesting" has been around for a long time. I think I first saw a water harvesting device in the U.S. Army Survival manual in the 1980s. It's an active research area and devices continue to improve.

Passive? Hydrophobic+Dessicant? dew collector? In the desert?

Dew collector seems to make the most sense for 1980

If we're being condescending: 'So, a parasol?'.

I wasn't trying to be condescending, just trying to point out that trees might not be the most viable structure. Last time I was in southern Arizona when I wanted some relief I'd just find a solar panel installation in a parking lot and hang out under that.