By contrast, deep wells have several putative advantages over qanats. First, deep wells are not limited by slope or soil conditions and can be located at sites convenient to transportation networks, populations centers, and markets. Second, they draw water from deep in the aquifer where seasonal variations in flow do not occur.
But deep wells also have disadvantages. The construction, maintenance, and fuel costs (for motorized pumps) of deep wells are high. Moreover, deep wells cannot be built
using local materials and local labor. By far the major disadvantage (and advantage) of deep wells, however, involves their success in meeting the growing need for water in the Middle East. Deep wells can draw water from permanent aquifers on demand without regard to rates of recharge. The technology, therefore, enables people to exploit their water resources in an unsustainable fashion. The ability of deep wells, and motorized pumps, to withdraw water in excess of an aquifer’s recharge rate makes this modern technology very attractive in the short term. As a result, however, water is fast becoming a non-renewable resource in areas where deep wells are used.
– From ‘Qanats and Lifeworlds in Iranian Plateau Villages’ by Paul Ward English.