An āb anbār is a traditional reservoir of drinking water in Persian antiquity. The Persian phrase literally translates as "water warehouse".
To withstand the pressure the water exerts on the containers of the storage tank, the storage itself was built below ground level. One important aspect to consider here is their resistance to earthquakes. Many cities in Iran lie in a region that have been struck with massive earthquakes. However, since almost all ab anbars are subterranean structures capped barely above ground level, they inherently possess stable structures.
The construction material used for ab anbars were very tough and extensively used a special mortar called sarooj made of sand, clay, egg whites, lime, goat hair, and ash in specific proportions, depending on location and climate of the city. This mixture was thought to be completely water impenetrable. The walls of the storage were often 2 meters thick, and special bricks had to be used. These bricks were especially baked for ab anbars and were called Ajor Ab anbari. Some ab anbars were so big that they would be built underneath caravanserais such as the ab anbar of Haj Agha Ali in Kerman. Sometimes they would also be built under mosques, such as the ab anbar of Vazir near Isfahan.
Ab anbars in Iran are known to have used anywhere from one to six windcatchers. Qazvin’s ab anbars however, do not frequently use windcatchers like in other parts of Iran, perhaps because of climatic conditions; Qazvin has very cold winters and not so hot summers like Yazd does. Most of Qazvin’s ab anbars are only equipped with ventilation shafts or semi-windcatchers. Ab anbars in Yazd, Kashan, Naeen, and other hot climate cities of Iran on the other hand extensively use windcathcers for cooling and ventilation purposes.
The way windcatchers work is that the moving air masses (wind, breeze, etc) at the top of windcatchers create a pressure gradient between the top of the windcatcher and its base, inside, at the bottom of the shaft. This pressure gradient sucks out rising hot air from inside the shaft while the colder dense air remains. The superb heat resistant material of the walls of the ab anbar further create an insulating effect that tends to lower the temperature inside an ab anbar, similar to a cave. The ventilating effect of the windcatchers prevent any stagnant air and hence any dew or humidity from forming inside, and the overall effect is pure, clean, cold water all year round.