Non-conventional urban water resources, water use and demand

Water scarcity is a critical issue facing the water sector worldwide, particularly in arid and semi-arid regions. Several factors, including climate change, population growth, and urbanization, drive water scarcity, leading to increased water demand and pressure on conventional water resources. Non-conventional water resources, such as urban rainwater harvesting, provide solutions to address these challenges. Urban rainwater harvesting (URWH) is a traditional and widely practiced technique that provides additional water at the household level and contributes to sustainable water management. Urban rainwater harvesting dates back to ancient times, but it has regained popularity in the last decade. Water quality is a critical aspect of the successful implementation of modern rainwater harvesting systems, as it determines the use options. Additionally, the tank size affects the efficiency and feasibility of the system. Ancient rainwater harvesting examples also provide valuable lessons for adopting and using rainwater harvesting as a sustainable strategy for managing water resources to address the water scarcity. The overarching objective of this dissertation is to evaluate the potential of urban rainwater harvesting (RWH) as a sustainable water resource. The specific objectives were as follows: (i) to evaluate the effects of rainfall data characteristics (both time series length and resolution) on tank size design, (ii) to assess the water quality of harvested rainwater, and (iii) to assess the hydrological performance of ancient cisterns in southern Jordan under current climatic and environmental conditions. In Chapter 2, the influence of rainfall data length and resolution on the design of rooftop RWH tanks is investigated in two case studies from two regions in Jordan and Germany. The findings indicate that long-term (≥30 years) and daily resolution rainfall records are required to capture temporal and seasonal variability. Using shorter and lower-resolution datasets led to inaccurate estimations of tank sizes, particularly in regions with highly seasonal rainfall, such as Jordan. In Chapter 3, a systematic literature review is conducted to assess the suitability of harvested rainwater for drinking and irrigation, as well as to review the main sources of contamination affecting water quality and the most common contaminants detected in rainwater. The results revealed that microbial contamination is the primary limiting factor for using water for drinking and irrigation, as it frequently exceeds the Jordanian standards. Emerging contaminants, such as microplastics and pharmaceutical residues, remain largely unexplored, and pre-treatment has received little attention in previous studies. In Chapters 4 and 5, a hydrological analysis was conducted to evaluate the hydrological performance of ancient cisterns at the As-Sila and Humayma archaeological sites under present climatic and environmental conditions using different runoff estimation methods and GIS analysis. The results showed that the As-Sila cisterns have very small catchments, while the Humayma cisterns are fed by larger contributing areas than those of As-Sila. Even though the estimated runoff values are lower than the sizes of the surveyed cisterns, this discrepancy is due to several factors, including that the estimated catchment areas in this study do not represent the original catchment areas from antiquity and that the hydraulic infrastructure that directed runoff into these cisterns no longer exists today. Another suggestion is that cisterns were deliberately oversized to capture extreme and rare events as adaptive strategies to cope with water scarcity and drought conditions in arid regions of the country. Overall, these cisterns remain hydrologically functional and provide valuable lessons for improving the resilience of modern rainwater harvesting systems. The overall findings of this dissertation highlight the importance of urban rainwater harvesting as a sustainable solution to water scarcity and climate change, particularly in semi-arid and arid regions. This was achieved by condensing different aspects of modern systems, including water quality and tank size, and learning from ancient rainwater harvesting systems. The results also draw attention to the importance of considering local contexts, such as local regulations and standards of water quality for the possible use of rainwater, as well as the temporal and seasonal variability of local rainfall when designing tank sizes. Furthermore, the findings illustrate how ancient systems were developed to address water scarcity and highlight the lessons that can be learned from these still-functioning ancient systems to improve the sustainability of modern practices in the region.