I grew up in a family with 6 kids. We had enough rainwater to cover all our needs (only had mains for emergency use). Solar powered house & no air con. (House was built in 1800s so doesn't need it) we had chickens, sheep and dad worked for a market gardener. My mum is the op-shop queen, and was a firm enforcer of Reduce Reuse Recycle.
Now the only thing they didn't do was make bio-fuel, but that's only because they didn't know about it back then (as in my parents didn't know).

Our little acre was totally self sustaining.
If everyone lived like that we wouldn't have to worry about population growth.