The work presents an example of a passive solar heating system, which utilizes direct solar energy to heat the water for domestic use. A passive thermosyphon heating system was designed, fabricated, and tested for its thermal performance in the semi-arid and four-season climate of the Faisalabad district of Pakistan. The heating system design was based on two-stage storage and natural thermosyphon circulation of water. An enhancement of the thermal performance of the thermosyphon systems by using a semicircular steel pot collector (covered with water carrying copper coil), two-step water storage, and side mirror reflectors was investigated. The experiments were conducted from April to July, 2014 when the ambient temperature was reported approximately between 30 to 45 degrees C. For the cited time duration, the cold-water temperature remained in the range of 18 to 25 degrees C. The maximum water temperature, during the intermittent flow mode operation of the system, remained between 48 and 88 degrees C. In continuous flow mode operation, the hot water temperature remained between 46 and 78 degrees C. Since water temperature in the range of 45 to 50 degrees C is considered suitable for domestic use, the presented design is acceptable for domestic use.