[nequo]

> It's hard to think of any civilizations that relied on mostly rainwater, but maybe I haven't heard of any.

I think that the Maya mainly relied on capturing rainwater for their water needs. I assume this would have included drinking water.

https://cnnespanol.cnn.com/2012/07/18/los-mayas-resolvieron-... (in Spanish)

https://www.discovermagazine.com/the-sciences/maya-water-sys... (in English)