Informative post @mercuriel, here are some interesting options I've heard about. Food; hydroponics. Japan unveiled a hydroponic farm that can grow 20,000 lettuce per day (soon to be 50,000) organically using much less water than traditional methods in the city center (reducing transport emissions too). Link here https://www.theguardian.com/environment/2016/feb/01/japanese-firm-to-open-worlds-first-robot-run-farm
Water; Singaporean NEWater, this is potable water produced from sewage water. Please see http://edition.cnn.com/2014/09/23/living/newater-singapore/index.html
There are also many, many desalination plants world wide (converting sea water into potable water). Although they are energy intensive, renewable sources can help mitigate this.
I hope one of the above taught you something new. Good post, upvoted and followed. If you have time to constructively criticize my latest post that would be great :)
Thanks a lot for all these links and ideas ! really interesting and perfectly in my "mindway" !