The first time I read about qanats, underground water canals that are used in many parts of the world for irrigation,was in connection with their destruction by the Mongols. But there is so much more to them than their destruction and (sometimes) eventual rebuilding.
The basic idea of a qanat system is to use groundwater for irrigation, but sometimes the water is or was used in urban areas too. Underground tunnels are used to carry groundwater to dry areas. Vertical tunnels are dug every so often for maintenance. Building and maintaining the qanats obviously is a major task. The link above has some diagrams and explains the principles behind the qanat system. They are an amazing system that requires a lot of community cooperation and engineering skill. But since Central Asian history isn't studied in the US, most people don't ever get to hear about these qanat systems.
There are many places where the qanat systems are still in use, including Iran, China, Yemen, and the Sahara. They were in use in Palestine until 1948 when the Palestinians lost most of their land. They are called qanats in Persian, kanerjing in Chinese, galerias in Spain, and more. The most common assumption is that the idea developed in Iran and spread with the Muslims and through trade to much of the world (including Mexico).
Karez is the word that is used in this part of the world. The western Chinese city of Turpan still has an extensive karez system and I hope to be able to see it in a few weeks. Many organizations are promoting the use of these traditional water systems. There are even international conferences on the qanats- the last one was just a week ago in Saudi.