Necessity is the mother of invention, especially in harsh environments. The Iranian āb-anbār is a perfect example. Designed as a roofed underground water cistern, ab-anbar is an ancient, creative, and exceptionally effective means of water preservation and cooling – only one of the various forms of reservoir that were invented to battle the harsh desert climate.
Rare and therefore precious, every drop of water needed to be preserved in the central and eastern deserts of Iran where poor rainfall and seasonal rivers caused extreme conditions in supplying potable water.
An-anbars were constructed to provide waterproof containers for a large volume of water while allowing for proper ventilation and access. These structures typically consist of an underground rectangular or cylindrical reservoir with a massive covering dome, one to six wind towers called wind-catchers used for ventilation and a staircase for the taking of water.
The construction began by first digging a cylindrical or sometimes rectangular tank deep into the ground, sometimes as much as twenty meters down. The walls of the tank were lined with bricks using a special type of impermeable mortar called sarooj that was made up of specific proportions of sand, clay, egg whites, lime, goat hair, and ash. As a result, the thick brick walls served as superb insulators, preventing both warming and freezing of the stored water. The tank was then covered with a dome that protected the water in the tank from evaporation and contamination from wind-borne dust and bird droppings.
Numerous domed masterpieces show that although challenging, placing a dome over the square plan was not something new to the Iranian architects. Some sources indicate that they would first construct the storage space and then fill it up with hay and straw all the way up to where they could start constructing the dome. After finishing the dome, they would set the straw on fire and clear the space inside. Holes seen on the walls of many cisterns show that scaffolding might have also been used.
In order to be strong enough to withstand both the huge pressure of the water stored and the earthquakes, which were rather common in the region, ab-anbars were deliberately constructed using special materials and below ground.
The latter was a required feature also because water flowed by gravity through man-made subterranean canal systems called qanats from the foothills of the surrounding snow-covered mountains and often over great distances directly into these reservoirs.
The wind-catchers (also known as badgir) that projected from the dome allowed for dry desert air to flow into and out of the dome, simultaneously cooling the water and preventing condensation on the inside of the dome which could lead to hygienic concerns. The main tank was entirely isolated from human contact.
In order to obtain water, one would go through the entrance (called a sar-dar) which would always be open and use a steep, barrel-vaulted staircase, running adjacent to the tank and leading down to the reservoir. Taps near the top of the stairs provided warmer water; in order to obtain the coolest water, one had to descend to the very bottom of the stairs. Often rooms or pavilions were built within the complex of the cistern to provide a comfortable resting place as well.
The person responsible for filling the ab-anbars was called a meerab. Once a year, the ab-anbar would be cleaned from settled sediments. Unlike the wealthy, who had private water reservoirs, the common person had to come and collect water themselves.
Given their importance to life in desert regions, it was crucial for ab-anbars to be public and located at the center of the cities, i.e., in each neighborhood. The common person would fill his own water container and carry it back home. This was an excellent opportunity for water carriers to make a living by delivering water from an ab-anbar in a goat skin bag strung over their shoulders and by selling it from door to door.
Large ab-anbars that served the users of caravanserais or places of worship were built directly under the edifice. Often built along caravan routes, the domes served as the only sure markers on desert routes.
The geographers of the 10th century described a fully functioning system of cisterns. While most of the existing ab-anbars are dated to the 18th and 19th centuries, the one in Yazd is considered to be the oldest and is dated 878/1473.
Until the history of ab-anbars is fully studied, it will remain unknown why architects in particular places chose perpendicular over cylindrical plans, since cylindrical spaces are easier to cover and are deemed more hygienic for water storage due to lack of any corners in the space. Furthermore, cylindrical tanks also have the advantage of containing a homogeneous pressure. Considering that the maximum diameter allowed by this method of construction is about 20 meters, the capacity of the traditional cylindrical cistern varies generally from 300 to 3,000 m3.
Although not evident at first glance, this traditional building technique is quite amazing. It took centuries of experience to develop such an ingenious technology that uses natural resources without any additional power. Widely used before the installation of public plumbing systems in the late 1950s, these underground structures remain fully functional to the present day. Nowadays, however, most of these remarkable structures are protected and pending restoration or used for touristic purposes while more than a few are falling into ruin and decay.