One of the most important operating parameters which affects the performance and efficiency of active solar stills is brine depth. In all of the previous experimental or theoretical studies, effects of water depth were investigated during only the first 24-hour period (or even shorter periods) of the operation of active solar stills. In other words, only the first day was taken into account. However, the production of an active solar still depends on several parameters such as brine temperature at sunrise (initial temperature), which are all affected by the depth variation after the first day of operation. However, the present research experimentally investigates the long-term effects of water depth on the performance of active solar stills for the first time. For this purpose, two parallel active solar stills coupled with solar collectors with different surface areas were fabricated and an experiment was conducted for 10 continuous days. Unlike previous studies, results indicated that the overall trend of distilled water production and efficiency increased with increased water depth. Hence, higher water depth is recommended for practical uses of solar stills (more than two days). (C) 2014 Elsevier B.V. All rights reserved.