Rainfall is the only source of groundwater recharge in arid countries, where no surface water exists. Quantification of the total volume of rainfall recharge is essential for water resources management, development and protection, but it is challenging. Numerous recharge estimation methods can be found in the literature, but the selection of the most appropriate one depends on the hydrogeological setting of the area of study and on the available data. Qatar is an arid country as rainfall is very little and surface water is non-existent. Aquifer is the only conventional source of water, which has been over-exploited in the last few decades. One of the main country's grand challenges is to implement an aquifer storage and recovery scheme, which requires understanding of the flow regime and quantification of the natural rainfall recharge. This study uses a water balance model coupled with Monte Carlo Simulation to quantify rainfall recharge. Using a historical groundwater piezometric map, the flow to the sea was calculated by applying Monte Carlo Simulation to the Darcy's Law. The natural recharge was calculated considering all water budget components. Results reveal the groundwater rainfall recharge amounts to 58.7 million m(3), which is close to literature values obtained by other means.