I'm working on a post-apocalyptic desert scenario in the near future where people live in small, loosely connected communities that trade with each other on a small scale and might have agreements regarding infrastructure use and maintenance and energy production such as establishing a smart grid. They are subsistence farmers and scavengers (to keep machines and computers running) but might cooperate for educational purposes and maybe even establish something along the lines of universities. They would be hampered by specialty and hard-to-make products not being available. Electricity generation would be completely decentralized and maybe not available around the clock. Clean drinking water would be infinitely more precious as even ground water might be salty. In general these communities would be very eco-friendly by necessity. Waste and pollution of common goods would be considered sin.
So the two biggest problems are the absence of fertile soil and water scarcity.
I imagine you could use solar heat to desalinate sea water and transport it inland using pipelines. I'm not sure how energy efficient this is (if it was cheap it'd be used in all desert regions with sea access on a big scale) and going high tech would defeat the purpose as there wouldn't be a central authority keeping large and complex infrastructure projects running, only agreements between small communities to say maintain a stretch of road or pipeline. Also the power-differential arising from control over water distribution by one group of people could lead to conflict. This is way big centralized undertakings are to be avoided. Solar pumps could pump up ground water to be desalinated locally if need be.
Do hydroponics present an answer in this situation or would you have to add other ways of growing food at the village level? You could farm vegetables and fish but you would need grain, right? Not just to make sure people get enough energy from carbs but also to feed it to livestock assuming an omnivore diet. I've never heard of hydroponics being used to grow grain. I also don't know how water efficient the technology is but I'm assuming it must be since NASA is working on it.
Seems there's a consensus that hydroponics is out because it's too high tech and that the solution will be combination of aquaponics, raised-bed-farming of vegetables, and the farming of rabbits, chicken, goats and insects for protein.
I didn't know saltwater aquaponics existed (even though there's no reason it shouldn't). This suggests that the most popular fish for sweetwater aquaponics can be modified to tolerate salt water. It makes protein (and possible vegetable) farming using salt water look quite feasible.
The question that remains is how to reproduce fertile soil. I'm assuming this can be done using compost? Could an agricultural cycle be established that removes the need to "fetch" natural soil indefinitely once it's been going for a while?