Lake Hawassa is one of the eight Major Ethiopian Rift Valley Lakes and the smallest among them, which is situated in southern regional state; it is a closed basin system and receives water from only perennial Tikurwuha River and runoff from the catchment areas. A water quality index (WQI) developed by the Canadian council of ministers of the Environment (CCME) was applied to Lake Hawassa. The present study was designed to determine the water quality status of the lake for drinking water use by employing the water quality index. To assess the status, water samples were collected in 15 days intervals for a period of 60 days from October to December 2015. From all water quality parameters analyzed the water quality of lake Hawassa falls under marginal category for drinking, which reveals the water is frequently threatened and impaired, and as well departs from natural condition.