It seems to me that the acequia are an open and distributed technology, so even when the central authority collapsed, each individual community was able to keep the services running based on that technology, for over a thousand years.

Modern irrigation is incredible, modern cities are amazing, modern software connects most humans on the planet. But ... we can learn.

You mean like this? https://en.wikipedia.org/wiki/Great_Man-Made_River

Droughts, there is simply not as much water as there used to be :(