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Understanding the connection between water supply and energy consumption in a circular economy is crucial for managing the demands of these resources. Sankey diagrams have the potential to enhance the visualisation of resource flows. However, there is a knowledge gap regarding the effective use of Sankey diagrams to capture the water-energy nexus and circularity of water. This study focused on effectively utilizing Sankey diagrams to model the nexus of water and energy flows and to assess the circularity of water. A comprehensive literature review was conducted on major studies on water material flows and modelling. This was supported by a review of approaches for modelling circularity, which have evolved from the material circularity index. The newly developed framework in this paper models water resource flows at all stages of the water supply chain, embedding the nexus as an interaction and considering resource intensity and material circularity index at each node. A city-level case study in South Africa was then used to apply the recommendations, model circularity, and the water-energy nexus using Sankey diagrams. In terms of circularity, the results indicate that water loss in the study area was very high, accounting for up to 40% of the total water supply and the water recycle rate was still very low, ranging from 3% to 7%. In terms of the nexus, the residential sector was found to have the highest energy intensity for water supply, primarily due to energy demand for water heating. Exploring the use of renewable or solar energy for water heating will be of interest and value. The new approach presented in this study allows for the simultaneous consideration of objectives, enabling a more robust analysis of energy-effective water use and water circularity along the water supply chain. [Display omitted] • A new framework for modelling the water energy nexus enriched by circularity options, energy intensity factors and confidence modelling. • Options for embedded circularity through the water supply chain. • The urgent challenge to address massive water loses in water supply systems for water scarce regions. • New Sankey diagrams showcasing how to model nexus and circularity. [ABSTRACT FROM AUTHOR]

Water supply in an increasing number of rural and peri-urban communities can be described as marginal i.e. subject to failure, becoming unaffordable or increasingly difficult to access. A range of common factors contribute to water marginalisation or access bias. Firstly, communities may be poorly served by formal water infrastructure by being on the margins of urban settlements. Secondly, where water infrastructure exists, this may be prone to failure as local municipalities and water utilities with limited capacity and resources struggle to maintain a widely dispersed system. Thirdly, when local water systems fail, they are often not repaired quickly, if repaired at all. This results in people, often with very limited resources having to obtain water from far distances or having to pay someone to transport water to them in order to meet their basic water needs. Thus, where water supplies are unreliable, unaffordable and difficult to access, geography, urban settlement patterns, the choice of water distribution systems, and the management capacity result in water marginality. This paper investigates water marginality in communities in rural and peri-urban areas in South Africa. It utilises surveys and interviews of communities, the local authority, water and urban planning officials, to understand the nature of this marginality, and investigates the key contributory factors. This forms the basis for recommendations on how access and marginalisation challenges can be addressed. The paper provides valuable insights on how, and why, water marginality occurs, and proposes strategies for sustainable solutions. As climate change and rural-urban migration accentuate water marginality, the study offers important and timely insights in an area that urgently requires further research. [ABSTRACT FROM AUTHOR]

This paper presents an integrated rainwater harvesting and greywater recycling system to tackle the energy-water nexus in residences with unreliable water and electricity supply. The system is made up of the municipal water and energy supplies, a rainwater harvesting system and a greywater recycling system to supply the residential water demand. A combined sizing and operational optimization approach is developed. In particular, a mixed integer linear programming model is formulated to determine the optimal sizes of the water tanks and optimal operation of pumps to reduce potable water consumption and electricity cost under the time-of-use tariff. The model formulated is applied to a practical case study of a single-family house in Durban, Kwa-Zulu Natal province of South Africa. Simulations results with measured rainfall intensity over five years show that the proposed integrated rainwater harvesting and greywater recycling system is beneficial for the household in terms of both water savings and financial cost savings with an acceptable payback period of 4.39 years. To investigate the validity of the results obtained in different applications, a sensitivity analysis was performed concerning uncertainties in water demand, rainfall intensity, the cost of electricity and discount rate. The findings confirm that the model developed is robust against uncertainties in these parameters. It is also concluded that payback period of the project can be even shorter if applied to a case with a higher water demand. • Develops an integrated rainwater harvesting and greywater recycling sys-tem. • Optimizes the sizes of tanks and operation of pumps for cost-e_ectiveness. • 56.46% potable water and 50.51% wastewater cost savings are achieved. • Reduces operating cost by 54.9% with a payback period of 4.39 years. • System performance is verified using measured 5-year rainfall data. [ABSTRACT FROM AUTHOR]