Abstract
Cities in South Africa are faced with increasing water scarcity driven by rapid urbanisation and increasing water demand that exceeds available water supply. The country’s economic hub, Johannesburg, is reportedly one drought away from a water supply crisis. Its vulnerability to water supply crisis is compounded by limited water resources, rapid population growth and high water consumption. Although water reclamation has proven to be a viable solution in some parts of the world, its adoption remains low and is yet to be incorporated into the mainstream of water supply for cities such as Johannesburg. One of the major reasons for low adoption is the complexity in the decision-making processes, which is often characterised by a web of interconnected socio-economic, institutional and technical factors. There are limited studies that integrate these factors holistically to inform decision-making for water reclamation systems. This study bridges this gap by adopting a systems dynamics approach to develop a decision-support model for assessing water reclamation options over a 20-year period. Causal Loop Diagrams (CLDs) were developed drawing insights from literature review and secondary data from the HSRC database to illustrate interconnections and feedback loops between water resources availability, together with social and techno-economic factors. Leverage points where policy recommendations could be formulated were illustrated in the CLDs, including enhancing wastewater quality, reducing blending requirements, and increasing public awareness. The developed system dynamics model comprises four subsystems, namely: the economic dimension, population growth, wastewater resource, and water demand. The model's applicability was demonstrated using Diepsloot Township as a case study. It was tested and validated using cross-sectional survey data from the Human Sciences Research Council (HSRC) and secondary data from reports, South African government agencies, and peer-reviewed literature.
The study findings show a high acceptance rate for water reclamation as an alternative source. Three scenarios were developed to simulate water reclamation options. The model's results show that, under the business-as-usual scenario, reclaimed water won't be sufficient to meet the water demand for the entire simulation period. The results of the three developed scenarios indicate that aligning water reclamation capacity with population growth results in higher economic returns and ensures adequate water supply for domestic and other uses. However, better planning and preparedness is required for successful water reclamation schemes and to minimise crisis response strategies. The findings highlight that the systems dynamics model is
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valuable for assessing water reclamation options in urban areas. Not only does it provide policymakers with a broader understanding of the complexities inherent in water reclamation systems, but it also enables informed decision-making for water utilities.
The study thus underscores the potential of integrated modelling approaches, such as systems dynamics models, to navigate the intricate interconnections of urban water reclamation systems.