The aim of this study is to improve the production of potable water through ultra modified double slope solar still (UMDSSS) by harvesting of direct solar energy as well as diffused radiation through transparent side walls. The setup was fabricated in combination with FRP and transparent acrylic sheets with a total basin area of 2 m(2). Reflectors angles (30 degrees, 45 degrees, 60 degrees, and 75 degrees) were optimized for climatic conditions of Lucknow (26 degrees 30' N, 80 degrees 13' E), U.P., India. On the basis of productivity, optimized reflector angle has been found as 60 degrees. The experimental and theoretical studies were carried out in the different seasons of year 2018. The basin water depth and glass cover tilt angle have been taken as 1.0 cm and 15 degrees respectively. Our experimental investigation shows that the cumulative distillate productivity was obtained as 9157 ml/day and 6630 ml/day during summer and winter season, respectively at 60 degrees reflector angle. The performance evaluation has been carried out in terms of physicochemical environmental parameters, productivity, and economic analysis. On the basis of economic analysis, the payback period was found 111 days and thermal efficiency of ultramodified solar still is higher 10.4% in summer and 10.0% in winter than that modified solar still.