About 130,000,000 and 4,500,000 million people live at an altitude between 2000-2500 and 3500-5200 above sea level respectively. Although, there are lots of water resources at high altitude which most of them are raw/ impure/saline water. Also, there is not enough research on the performance of small-scale solar desalination systems at highlands. The main purpose of this paper is to present the impact of altitude on the performance of a single slope single basin solar still. Two identical passive solar still at the top of Mount Tochal and city of Tehran with 3964 and 1171 m of height are tested respectively. A series of experiments during four days from 24.07.2018 to 27.07.2018 are performed. All experiments are conducted by considering the effect of all important environmental conditions and performed by two separate teams at the mountain and Tehran simultaneously. All experiments were started and ended at the same time. Findings show that maximum hourly yield at the summit of Tochal and Tehran reaches to 720 and 500 ml/m(2)/h respectively. Total productivity at the mountain is higher by about 56.1% rather than that in Tehran. The cost of produced water at Tochal and Tehran evaluated about 0.0112 and 0.0087 $/liter/m(2) respectively.