The design, analysis and modeling of solar energy-based water purifiers, commonly known as a solar still, which is based on the greenhouse effect, is the requirement of time as there is a scarcity of freshwater throughout the globe. The technology of purifying dirty water using solar energy is a promising solution for simplifying contemporary water scarcity as this technology does not create any bad effect on the surroundings, unlike conventional water purification technology, which creates a lot of polluting elements and ultimately has become problematic for the environment. Most solar energy-based water purifiers are self-sustainable, and they can be installed in remote locations where sunlight and source of impure water are available in abundance. This solar energy-based technology of water purification should perform better in hilly locations as the intensity of light is higher than the intensity of light in fields. The current chapter deals with the thermal modeling of different types of passive and active solar stills, including solar stills loaded with water-based nanofluids, followed by their energy and exergy analyses.