Assessment of rainwater harvesting potential from rooftops in Jordan’s Twelve Governorates

Rooftop rainwater harvesting (RRWH) offers a potential solution to Jordan’s pressing water scarcity problems. Yet, its feasibility and benefits necessitate a thorough assessment, particularly as existing studies on the subject are outdated and often constrained by limited scope or small data sets. To this end, our study assessed the potential of RRWH in Jordan's 12 governorates, utilizing historical rainfall data from 1987 to 2018 and official statistics on population and rooftop areas. The analyses used the Ripple Method and Water Balance Model to determine potential harvestable water volumes, potential water-saving percentages, and optimal tank sizes under different scenarios (i.e., using rainwater to meet the total consumption or only for toilet flushing). The findings reveal that Jordan has a total potential for rooftop rainwater harvesting amounting to 23.74 Mm³/year, corresponding to 4.54% of the total water demand. Should RRWH be implemented across all rooftops, the projected financial savings for Jordan could range from $170 million to $678 million. Among the governorates, Irbid and Amman have the highest potential, with estimated yields of 7.754 Mm³ and 8.453 Mm³ per year, respectively. Based on the best results for the scenario where harvested rainwater is only used to flush toilets, the optimal tank sizes for storing rainwater were estimated to be 2.7 m³ and 2 m³ per household in Ajlun and Irbid, respectively. For a regularized case (October–May), a payback period of 12.5–24 years based on desalination cost was found for an RRWH system capable of meeting thrice the flushing needs of a household. RRWH was showcased as a sustainable solution to Jordan’s water scarcity, emphasizing the necessity for broader implementation.