You’d have to find people who knew how to do those things. Cisterns, aqueducts, and even farming didn’t just happen, they developed over time of people figuring out small things, and passing on the information generation after generation and building on the knowledge slowly. For the vast majority of human history, we didn’t do these things.

Take ten or twenty random people from modern society and see how many of them know how to grow plants in a harsh environment and good luck getting one who knows how to work with stone. Just look back into our past, even relatively modern history, how often groups of people who were experienced farmers with passed down knowledge were almost, or actually were, starved out by the environment. Surviving is hard, even for those who have practised it. Modern society has made us forget that. Nature is waiting to own us again, and when she does, it will be brutal and nowhere near as easy as you make it sound. There’s a reason we almost went extinct numerous times.

If you could hand pick a group of survivors, sure you could make a community, but you don’t get to hand pick. You get who you happen to meet out of those who happen to survive which means random, which means good luck keeping the required skill sets alive.