Groundwater resources worldwide are under increasing stress, particularly in arid and semi-arid regions. Urbanisation, intensive agriculture, and industrial development place heavy pressure on the fossil groundwater, resulting in depletion of major aquifers worldwide, with more severe consequences in arid regions such as Saudi Arabia. This study aims to evaluate the feasibility of Treated Wastewater (TWW) for sustainable managed aquifer recharge (MAR) in the eastern coastal region of Saudi Arabia using an experimental approach. Twelve 1D MAR experiments were conducted to assess the efficiencies of various treated wastewater effluents for groundwater replenishment in the coastal sandy aquifer in the eastern region of Saudi Arabia. Three recharge scenarios (low, medium, and high) and two types of TWW (tertiary and secondary) were evaluated to optimise the MAR system. Clogging materials and water quality change were evaluated to determine the optimal recharge scenario. The results showed that the tertiary treated wastewater with low recharge scenarios was the optimal case with minimal impact on groundwater quality and aquifer integrity. In contrast, the high recharge scenarios with either tertiary or secondary treated wastewater showed a significant reduction in the hydraulic performance of aquifer materials, thus, the efficiency of the recharge system. The study found that the tertiary treated wastewater from the eastern region of Saudi Arabia is suitable for aquifer recharge with minimal pretreatment to remove nutrients, ions, and emerging contaminants (e.g., microplastics). The study findings provide insights into effective water resource management strategies that reduce water scarcity risks and strengthen long-term water security in arid environments. Moreover, the study demonstrated that implementing MAR with TWW can reduce non-renewable groundwater withdrawals by up to 30% in eastern Saudi Arabia, mitigating aquifer depletion and ensuring a more sustainable water supply.