Low knowledge retention in medical students is a problem in the health education sector. Retention itself is a reflection of memory ability which can be influenced by an individuals hydration condition. Therefore, this study aims to determine the effect of daily consumption of drinking water on retention in medical students. This research was a descriptive analytical observational study with cross-sectional design. Consisted of 59 medical students from Airlangga University who were divided into two groups: 34 students with water consumption ≥ 2L/day (57.63%) and 25 other students with water consumption < 2L/day (42.37%). There was score decrease from 1st semester test to 4th semester test in both groups, but it was not significant in students with poor hydration (p=0.059). However, average scores both in the 1st and 4th semester were higher in students with good hydration. The findings of this research also showed that students with water consumption ≥ 2L/day had less knowledge retention compared to other groups, but this finding wasnt significant as the pvalue was 0.320.