Mentha aquatica is an important traditional herb in north Iranian cuisine and folklore medicine, with high potential for storage as dried leaves. This study examines how different storage conditions and times affect the essential oil percentage and components of dried M . aquatica. Samples were collected from M. aquatica flowering branches at a natural habitat. The experiment had two storage treatments, i.e., refrigeration at 4 ± 1 °C and storage at 25 ± 2 °C with adequate airflow. There were three storage durations, i.e., 60, 120, and 365 d after drying, and three drying methods, i.e., shade-drying at 25 ± 2 °C, oven-drying at 40 °C, and microwave-drying at 200 W. The essential oil components decreased through storage duration, which was more noticeable in samples stored at 25 ± 2 °C compared to those stored at 4 ± 1 °C. Additionally, the type and amount of essential oil components differed under various storage conditions. The main compound in M. aquatica essential oil was 1,8-cineole, with its highest content (26.55%) in ovendried samples. The second-most prominent essential oil compound was trans-caryophyllene, with a high content in shade-dried plants stored at 25 ± 2 °C for 120 d and a lower content in samples dried with a 200 W microwave, followed by storage at 2 ± 4 °C for 365 d. The optimal treatment for maintaining more of the essential oil components was oven-drying at 40 °C and storage at 25 ± 2 °C. In sum, the current research showed that M. aquatica optimally retains its EO components when the foliage is oven-dried and subsequently stored at 2 ± 4 °C. This finding can benefit the EO industry in harvesting M. aquatica on a sustainable basis through drying and storage.