Energy crisis and water born diseases caused by impure water are two major concerns of the present era. Various techniques have been used to make saline/brackish water potable. Filtration, precipitation, sterilization, chemical treatment, etc. are some processes that remove macro impurities from impure water. Distillation is thermal energy‐based process that effectively removes contaminants from impure water. Reverse osmosis is a membrane‐based technique widely used for the purification purposes. Electrodialysis, Ion‐exchange, and Freezing are some other processes used to get soft/distilled water for various commercial and domestic uses. Most of the desalination techniques utilize energy from the nonrenewable energy sources. Solar distillation is one of the solutions of getting potable water using solar energy. Solar distillation unit coupled with thermal collectors, photovoltaic panels, and concentrators makes the system active and increases the distillate three to six times than conventional units. Multistage, multieffect active solar still is observed to give an average distillate output of 20 kg/m2/d. Economic analysis also shows that active solar still is a good replacement of nonrenewable energy based water purification techniques. In this article, different water desalination techniques with their economic analysis are briefly discussed. Detailed comprehensive review of researches carried out on active solar still system considering their designs, performance parameters, different hybrid combinations, along with challenges, opportunities, future scope of improvements have also been highlighted. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 444–464, 2018

The simplest and easily accessible type of solar distillation is passive solar still which utilizes freely and abundantly available sun energy for removal of salinity/impurity from saline/brackish water. The main drawback of passive solar still is its lower efficiency and distillation output. Different designs of passive solar stills are fabricated and tested by various researchers to meet water demand economically. Concave wick basin pyramidal-shaped solar still was observed to produce 4.0 l/m 2 /day average distillate with a cost of 0.065$/l. Double basin solar still showed an average of 85 % higher yield than single basin still. Stepped type, inclined, tubular, pyramidal, spherical, and hemispherical shapes were considered an efficient designs of passive solar still. Numbers of parameters such as water depth, solar radiation, ambient conditions, condensing cover material, its cooling and direction, internal and external reflectors, sun tracking system, wicks, thermal and energy storage materials were outlined which highly affect the performance of solar still. Water depth of 0.04 m and condensing cover inclination to latitude of the place were observed optimum operational parameters. A distillate output of 4.3 l/m 2 was collected with cotton gauge top cover cooling to V-type solar still. Increase of 75 % in productivity and 56 % in daily efficiency was observed with internal reflector stepped solar still. An improvement of 380 % was observed in stepwise basin solar still integrated with sun tracking system. Despite large efforts carried out on passive solar distillation, there are some challenges like bulkiness, high initial cost, and optimization of spacing between condensing cover and water surface of inclined still, thermophysical properties of basin material, flow rate, insulation material and its thickness, which need to be improved to make this technique efficient in practical utilization. This review paper mainly presents the results of previous work carried out on the designs, operational and process parameters affecting distillation, cost analysis, further scope of improvement in preceding work along with their limitations. The decade reviews on solar stills based on different context authored by many researchers have also been summarized. Moreover, this review paper will help the researchers to understand the basics of solar still with the need, developments and challenges in passive solar distillation to improve its thermal performance.

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