Solar thermal water purification systems offer sustainability by harnessing solar energy to drive the process of impure water purification. Passively driven solar thermal water purification systems like solar stills have been the preferred choice, particularly for remote regions with limited resources but high solar energy availability. The current chapter first briefly overviews solar stills, including their construction and working principle, which facilitates the evaporation of impure water and subsequent condensation into purified water. Next, we discuss the critical parameters influencing the freshwater productivity of solar stills through energy balance equations and various parametric experimental investigations. However, the freshwater productivity and overall thermal efficiency of conventional solar stills are low due to inherent parasitic losses associated with the impure bulk water and the ambient environment. Hence, specific enhancement techniques like the addition of solar collectors, heat storage materials, nanofluids, external heat sources, and condensation enhancement through surface texturing have been discussed. Moreover, the integration of heat pipes and evacuated tube solar collectors has also been introduced to improve heat absorption and distribution within the system. Finally, the challenges and future scope for making solar stills a commercially and economically viable option for a decentralized solar water purification system have been discussed.