Passive solar stills typically generate most of their distillate later than their solar radiation maxima, but such late day activity is often concealed if the performance is assessed on daily basis or based on water temperature. This study considers a single slope passive solar still operating under an evaporation chamber aspect ratio of 1.53 and relative humidity of 77.5%. The key issue of this study is what hourly values determine the ability to maintain the collection of distillate when the radiation falls, and whether the aspect ratio and the chamber humidity have the same physical basis. The data set consists of ambient temperature, solar radiation, wind velocity, cover temperature, water temperature, basin temperature, hourly distillate production and thermal efficiency from 09:00 to 17:00. The analysis employs temperature differences between basin and cover and water and cover, hourly distillate production normalized to solar radiation, percentage of post-peak generation of distillate, retention of basin-cover difference in the afternoon and normalized trajectory matching hourly yield. The still generated 3.66 l m−2 of distillate during the day, having its hourly maximum at 13:00 – 0.61 l h m−−2. During the period from 13:00 to 17:00, the solar radiation fell by 46.1%, and the hourly distillate yield by 34.4%, accounting for 70.8% of the daily distillate. The basin-cover temperature difference maintained 93.0% of its daily maximum during the afternoon, and the normalized hourly distillate production in 13:00-17:00 was 1.42 higher than in 10:00-12:00. For the whole day, the correlation coefficient of hourly yield vs. basin-cover difference is 0.870, but for 10:00-17:00 without the point 09:00 it is only 0.594. Physical meaning, therefore, cannot be expressed just by maximum temperature concept. While the main effect of high aspect ratio is increasing of the internal thermal state, lower chamber humidity can increase distillate production despite lower basin and water temperatures.