Why did Tehran depend on qanats for its water supply until 1933?

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Tehran relied on qanats for its entire water supply until 1933 primarily because the city is not situated near any major rivers.12

In arid regions like Iran, qanats were an essential water supply system developed to tap into underground mountain water sources. By constructing a series of gently sloping tunnels, these systems used gravity to channel water from distant alluvial fans or mountain sources to urban areas. This technology allowed cities to thrive in environments where water was otherwise scarce, serving as the primary method for providing water for both irrigation and domestic use until more modern infrastructure, such as dams on the Karaj, Jajrud, and Lar rivers, was developed to meet the needs of the growing population.3241