A few weeks ago I wrote about Sundrop Farms and their high-tech systems for growing food in the deserts. They use solar power to create fresh water from the sea, and then use it to irrigate and cool large greenhouses.
There are also older ways to grow food in the desert, using irrigation. One of the most intriguing is the Turpan water system in Northern China. It is a huge network of canals that moves meltwater from the mountains down to the dry lowlands, making agriculture possible in an otherwise unproductive landscape. The system consists of over a thousand vertical wells which are linked by underground tunnels, stretching over 3,000 miles. Keeping the canals underground protects them from sandstorms, keeps the water cleaner and reduces evaporation, making them more efficient (also see India’s solar canals project).
Remarkably, the system was built over 2,000 years ago, and it is still working today, bringing drinking water to communities and irrigation to the region’s vineyards. It is considered to be one of three ancient engineering masterpieces in China, the other being the Grand Canal and the Great Wall. A bit like London’s Victorian sewer system or India’s lost and rediscovered stepwells, underground architectural heritage is easily overlooked.
Here’s a little National Geographic video, if you want to see what it looks like:
The Earthbound Report 
The Nabateans used rainwater collection, and, if I recall, dew harvesting.