Considerable amount of surface water in Lebanon is stored behind dams, and the Qaraaoun Reservoir (QR) is a typical example. It is the largest surface water body in Lebanon where it irrigates 27,500 ha and generates 22% of Lebanon’s electricity. The reservoir is fed directly from the Litani River which receives water from several springs and from groundwater where both are replenished mainly from snowmelt. However, the relationship between snow cover area on the surrounding mountains and the water volume in the reservoir has not been investigated. This study aims at determining the influence of snow cover area as a water feeding source and the volume of water in the QR. The relationship between these two variables was calculated using satellite images (MODIS-Terra with 500 m spatial resolution) which enable retrieving measures each 8 days, and the in situ measuring instruments fixed in the QR. The investigated period was between 2001 and 2018. Results show that the water volume in the QR is substantially controlled by the snow cover area on the surrounding mountains. It was found that the average time period between snow accumulations on these mountains and the remarkable increase in water level in the QR is about 3 months, while the dynamic changes in snow cover (accumulation/melting) and the induced water level in the reservoir were calculated. In addition snow-water equivalent (SWE) was also determined. This study reveals the significance of snow cover, which either directly feeds the streams or indirectly replenishes the groundwater aquifers where both contribute in the water volume of the QR. Therefore, the catchment mountainous area where snow accumulates should be protected from human interventions which have been lately increased and impacted the hydrologic regime between snow cover and water volume in the QR.