RENEWABLE ENERGY AND WATER SUSTAINABILITY Feasibility of rainwater harvesting for sustainable water management in urban areas of Egypt Tamer A. Gado 1 & Doaa E. El-Agha 2 Received: 17 April 2019 /Accepted: 12 September 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Egypt’ s limited water resources, rapid population growth, and climate change are increasing the gap between water demand and supply. Meanwhile, significant amounts of rain fall in some regions in Egypt during specific storm events, which in some cases, lead to disasters like flash floods and inundations. Rainwater harvesting (RWH) can be considered as a sustainable promising solution to water shortage and inundation problems. In this work, the feasibility of RWH for urban areas was assessed over 22 cities throughout Egypt. Results show that the annual volume of rainwater harvested can reach 142.5 MCM in the considered cities, provided that all rain falling on the urban areas is collected. High potential of rainfall harvesting was found for cities that located on the North Coast, e.g., the potential water saving from the share of RWH in Alexandria can satisfy around 12% of its future supplementary domestic water needs. In contrast, rainfall over the cities located on the middle and the south of the country is insignificant to be harvested. A case study for the 5th settlement region in Cairo was discussed in terms of groundwater recharge and surface runoff estimation for two conditions: No–RWH and RWH systems by implementing recharge wells to store rainwater into the aquifer. Land cover classification maps of urban areas were created by using the ARCGIS software to estimate equivalent infiltration coefficients. The results demonstrate that the implementation of such RWH system has a significant impact on the regional water cycle, where the effective infiltration coefficient increased from 10% (No–RWH) to 75% (RWH) in the case study. Accordingly, the runoff coefficient decreased in the case study from 0.8 (No–RWH) to 0.15 (RWH), and the volume of runoff decreased in the case of RWH by around 82% lower than that of the No–RWH condition. Thus, direct infiltration of RWH into an aquifer can play an important role in sound water management for urban environments, as this may lead to a significant reduction in risks of flooding and expenses of municipal drainage systems installation and operation. Keywords Rainfall . Rainwater harvesting . Groundwater recharge . Water management . Infiltration coefficient . Water savings . Egypt Introduction Scientists warned that the gap between demand and supply in many countries could exceed 40 percent due to threats of climate change and population growth within 20 years (Daily Mail 2011). Particularly in Egypt, renewable water resources are considered limited and rely mainly on the Nile River (55.5 BCM/year) (billion cubic meter per year) that represents 97%. Meanwhile, Egypt population are growing rapidly (2% annually) (World Bank 2017), causing stress on water resources due to increased water requirements for do- mestic consumption and increased use of irrigation water to meet higher food demands. In year 2015, the population reached 90 million while water availability was 611 m 3 / capita/year; and the population is expected to reach 140 mil- lion by the year 2037 and water availability will be 392 m 3 / capita/year (MWRI 2015). Therefore, developing water con- servation techniques and controlling water pollution have be- come necessary to meet current challenges facing scientists, engineers, and policy makers as the comprehensive Responsible editor: Philippe Garrigues * Tamer A. Gado tamer.gado@f-eng.tanta.edu.eg; tamergado@hotmail.com Doaa E. El-Agha doaaezzat777@gmail.com 1 Department of Irrigation and Hydraulics Engineering, Faculty of Engineering, Tanta University, Tanta, Egypt 2 Department of Civil Engineering, Higher Institute of Engineering and Technology, Kafr El-Sheikh, Egypt Environmental Science and Pollution Research https://doi.org/10.1007/s11356-019-06529-5