In Rajasthan, a region known for its arid climate, various water harvesting methods are employed to combat water scarcity. Option 1, Johads, are small earthen dams that capture rainwater and help recharge groundwater. Option 2, Khadins, are traditional rainwater harvesting systems that involve diverting and storing rainwater in low-lying areas. Option 4, Tanka, is an underground tank used to store rainwater.

Option 3, Guls or Kuls, is not a water harvesting method used in Rajasthan. This is incorrect as Guls or Kuls are actually an ancient water management system found in the mountainous regions of India, particularly in the state of Jammu and Kashmir. These channels are used to divert water from streams and rivers to irrigate fields and gardens.

Alert - correct answer should be 3