1 Introduction

In Africa, energy, water, and food insecurity pose significant challenges, with millions in informal settlements facing heightened vulnerabilities due to overcrowding, poverty, and inadequate infrastructure. Despite historical neglect, the intersection of water, energy and food insecurity in cities has profound social, economic and environmental implications. This highlights the pressing need for immediate solutions to combat the triple challenge of water, energy, and food insecurity. Recently, there has been increased academic and policy focus on the practical potential of decentralised Water-Energy-Food (WEF) systems in addressing the three distinct, yet kindred problems: energy, water, and food insecurity in Africa [1,2,3].

Despite constraints related to decentralised WEF systems, including high capital costs, technical and institutional limitations, low reliability, and non-workable business models, there are working examples of these systems emerging worldwide [1,2,3]. Haji et al. [2] introduced a computational decision framework to achieve sustainable and resilient decentralised water, energy, and food systems at the national level in Qatar using the ‘WEF nexus node’ approach, demonstrating optimisation of location, operation at a minimum cost, and risk reduction of existing WEF nodes. Using the case of Neil Island, Thomas et al. [3] demonstrated how solar thermal energy-based cogeneration and polygeneration systems have the potential for intervention in marginalised communities’ livelihoods with a focus on the energy-land–water-food nexus. Another study by Winklmaier and Bazan Santos [4] on rural electrification in sub-Saharan Africa through the least-cost modelling of decentralised Water-Energy-Food systems in Zimbabwe demonstrated the techno-economic benefits of decentralised Water-Energy-Food systems. A pilot project in Morocco’s Youssoufia Province also demonstrated the benefits of decentralised renewable energy initiatives in developing nations [5].

This study focuses on decentralised Water-Energy-Food in the South African context. South Africa faces multiple challenges, including water, energy, and food crises, making it ideal to investigate how marginalised communities navigate them. Specifically, the city of Johannesburg. Although it is one of South Africa’s most vibrant cities, it faces many socio-spatial divides inherited from the colonial-cum-apartheid government [6]. Currently, Johannesburg is plagued by severe water crises, with some analysts anticipating a day zero, as happened in Cape Town in 2018 [7]. The water crisis is severe in the southern suburbs where the poor reside. Likewise, since 2020, the energy crisis through load-shedding has persisted in Johannesburg, like elsewhere in South Africa [8]. Although the government seems to be taking some action to address this energy problem, the problem’s geo-political nature, riddled with political economy issues, exacerbates the situation with no tangible plan in sight [9]. Again, the urban poor bear much of the brunt of this energy crisis as they are forced to fork out more to buy alternative energy sources such as gas, paraffin, and charcoal, with their disadvantages. Ultimately, water and energy challenges also impact the food system in Johannesburg.

Rapid urbanisation, migration—particularly of foreign undocumented migrants [10, 11], segregatory urban planning that marginalises the poor, and the unavailability of affordable low-cost housing are forcing the underprivileged population into overcrowded slums in South Africa [12, 13]. In informal settlements like Diepsloot in South Africa (the focus of our study), residents grapple with a web of interconnected challenges spanning water, energy, and food security. Limited access to clean water sources and inadequate sanitation infrastructure heightens health risks. While unequal water distribution exacerbates its scarcity during droughts. Energy shortages and frequent load shedding disrupt daily life, forcing reliance on informal and often hazardous energy sources. High energy costs further strain already limited budgets of the poor. Similarly, food insecurity persists due to restricted access to nutritious options, exacerbated by the lack of agricultural land and price volatility. These challenges intertwine, perpetuating cycles of poverty and environmental degradation. The resulting health implications underscore the urgent need for holistic interventions addressing the root causes of water, energy, and food insecurity to foster sustainable development in these marginalized communities.

Our study aims to show the potential of decentralised Water-Energy-Food systems in promoting access to food, water, and energy in informal settlements in Africa. This objective is achieved through space analysis, least-cost modelling of sack farming, and establishing renewable energy technologies in the Diepsloot slums of Johannesburg, South Africa. We integrated proven methodologies to address water, energy, and food challenges at local level. By adapting sack farming techniques and assessing local resources through GIS and climate data, we optimize crop selection and water usage. Using least-cost modeling, we design efficient energy systems for a community centre and proposed passive cooling solutions for the marketplace. Additionally, we explored the integration of renewable energy sources like solar power to enhance sustainability. Through these innovative methods, we aimed to provide practical solutions for improved water-energy-food security and socio-economic development in marginalized communities like Diepsloot.

One of the comprehensive studies in South Africa by Mabhaudhi et al. [14] on the state of the WEF nexus revealed that South Africa has many opportunities to implement WEF projects through solar power generation, water reuse, and recycling, and precision agriculture in alignment with the SDGs, particularly SDGs 2 (zero hunger), 6 (clean water and sanitation) and 7 (affordable and clean energy). However, their study pointed out a paucity of research aimed at demonstrating the applicability of the WEF nexus at the local level, especially among the poor. In addressing the research gap highlighted by Mabhaudhi et al. regarding the applicability of the WEF nexus at the local level, our study takes a unique, focused and practical approach. It acknowledges the broader challenges and opportunities outlined in existing literature on decentralised WEF systems. It also directs attention to a specific informal settlement—Diepsloot in Johannesburg, South Africa. By employing space analysis, least-cost modeling of sack farming, and integrating renewable energy technologies, our research aims to provide practical and localized solutions to water, energy, and food insecurity. Through this targeted approach, we seek to bridge the gap between theoretical discussions and on-the-ground implementation, demonstrating the tangible benefits of decentralized WEF systems for marginalized communities.

The study hypothesises that implementation of decentralized WEF systems, integrated space analysis, least-cost modeling of sack farming, and renewable energy technologies in the Diepsloot slums of Johannesburg, South Africa, will lead to improved access to essential resources, enhanced socio-economic development, and increased environmental sustainability in the community. The specific objectives of the study are:

  • To assess the feasibility and effectiveness of decentralized WEF systems in addressing water, energy, and food challenges in informal settlements, focusing on the Diepsloot slums of Johannesburg, South Africa.

  • To apply space analysis techniques to identify optimal locations and resource utilization for WEF system implementation in Diepsloot.

  • To utilize least-cost modeling to design efficient and sustainable energy systems for community centers and passive cooling solutions for marketplaces in Diepsloot.

  • To integrate renewable energy technologies, such as solar power, into the WEF systems to enhance sustainability and resilience in Diepsloot.

2 Decentralised Water-Energy-Food (WEF) systems

Water, energy, and food security are intricately related and have strong inherent interlinkages [15]. Following this growing realisation, the Bonn Nexus Conference called for a nexus approach to addressing WEF challenges [16]. The WEF security nexus (Fig. 1) is a conceptual framework that describes the interconnections among water, energy, and food systems and seeks to develop joint solutions that mitigate the tradeoffs and promote synergies among these three sectors [16]. In addressing WEF security challenges, adopting a nexus approach is crucial for developing holistic solutions that acknowledges the interconnected nature of these sectors. This approach recognizes that water availability directly impacts food production and energy generation, while energy access is essential for sustainable development and resilience, particularly in marginalized communities like Diepsloot.

Fig. 1
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Source: Authors

Water-energy-food (WEF) nexus.

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The nexus of water, energy, and food sectors affect how WEF security can be simultaneously achieved [17]. Water security is defined in the sustainable development goals as “access to safe drinking water and sanitation,” which has recently become a human right through the United Nations General Assembly’s Resolution A/RES/64/292 [18]. Access to water is critical and central to building adaptive capacity to climate change among marginalised communities [19]. The role of water in contributing to food production has been shown in several studies, including water for irrigating crops, cooking, and maintaining health and well-being [20, 21].

Energy security is defined as “access to clean, reliable, and affordable energy services for cooking and heating, lighting, communications, and productive uses,” [22] and as “uninterrupted physical availability [of energy] at a price which is affordable, while respecting environmental concerns” [22]. Access to modern energy is vital for sustainable development. In marginalised communities, decentralised energy solutions may significantly reduce poverty, support community institutions, and facilitate the generation of basic services such as communication, water access, education, and health services. However, most dwellers in off-grid communities in developing countries have little or no access to modern energy technologies, although they are endowed with a vast potential for renewable energy resources. Decentralised energy solutions could serve as an option to solve this energy access problem [1, 23].

Food security is defined by the Food and Agriculture Organization (FAO) as “availability and access to sufficient, safe and nutritious food to meet the dietary needs and food preferences for an active and healthy life” [24]. Adequate food has also been defined as a human right. The emphasis on access in these definitions also implies that security is not so much about the average (e.g., annual) availability of resources; it must encompass variability and extreme situations such as droughts or price shocks, and the psychological resilience of the poor, including those residing in informal settlements like Diepsloot, in South Africa. By adopting a decentralized approach that considers the interplay of water, energy, and food systems, practitioners can develop more resilient and sustainable solutions that enhance the well-being of communities in informal settlements and beyond.

3 Description of the study area: Diepsloot, South Africa

Diepsloot (Fig. 2) is a rapidly growing and popular informal settlement in South Africa. Diepsloot was established in 1995 as a relocation area for informally settled households from Zevenfontein [25]. It is located on the northern edge of the Johannesburg metropolitan area, approximately 40 kms from the inner city and 20 kms north of Sandton, close to Fourways and the Midrand corridor [26]. Diepsloot has approximately 62,882 households with a population density of 11,532 persons/km2. It is now home to about 138,329 people; many live in shacks 3 × 2 m2 assembled from scrap metal, wood, plastic, and cardboard [25]. As a dense, unplanned, and impoverished settlement, Diepsloot is starkly contrasted with its surroundings comprising the high-income private sector, residential and commercial developments such as estate housing projects, business parks, shopping centres, and office developments.

Fig. 2
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Source: Authors

Diepsloot, South Africa.

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Diepsloot is inhabited by people from different tribes, cultures, traditions, and nationalities [27]. Many young and upcoming adults make up 55.9% of the population [25]. Those economically active comprise 73.7% of the population, 47% of whom are employed in most elementary or blue-collar occupations, including craft and related trades, service work, shop and market sales, and machine assembly [25]. Diepsloot residents experience low to moderate living standards, 52.4% in the LSM 1–3 category and 34.6% in the LSM 4–5 category. 29% of the population is severely food insecure [25]. Despite its socio-economic challenges, Diepsloot is a vibrant neighbourhood with optimistic residents determined to improve their lives. Many active community development organisations exist in Diepsloot, including Ikamva Youth Diepsloot, SayPro Diepsloot, Global Hope Youth Foundation, and diepsloot [27].

Diepsloot was chosen as the study area due to several key factors that influenced this selection. Firstly, its status as a rapidly growing and popular informal settlement in South Africa highlights its relevance in understanding the complexities of urban development in marginalized communities. The area’s dense, unplanned layout, combined with its high population density, exacerbates issues related to water, energy, and food security. Secondly, Diepsloot’s stark contrast with its affluent surroundings, comprising high-income private sector developments and residential estates, demonstrate the socio-economic disparities and challenges faced by its residents. Additionally, the specific challenges presented by Diepsloot, including widespread poverty, inadequate infrastructure, and high levels of food insecurity, make it a compelling site for interventions aimed at improving water, energy, and food security.

4 Methods

We reviewed best case studies on sack farming in urban slums like Kibera in Kenya and adapted the approach for Dieploot. To estimate groundwater availability, GIS data was utilized, integrating factors such as topography and land use to assess aquifer potential and recharge rates. Furthermore, soil data, including texture, pH, and nutrient content, were analyzed alongside local agricultural habits to determine suitable crops for cultivation. This involved considering factors such as crop water requirements, growth cycles, and yield potentials. Climate characteristics were incorporated into the study’s design through a comprehensive analysis of the Köppen-Geiger climate classification [28], which provided insights into Diepsloot’s climate zone and prevailing weather patterns. This information was further refined by integrating local meteorological data on precipitation and temperature distribution. AquaCrop, a crop modeling tool developed by the Food and Agriculture Organization (FAO), was then employed to simulate crop growth under varying climatic conditions, enabling the assessment of production efficiency and water requirements at different stages of development.

Validation of models, including AquaCrop and the linear optimization model urbs, was conducted through rigorous testing against empirical data and field observations. AquaCrop's accuracy in predicting crop water requirements and yield potentials was verified by comparing model outputs with actual crop performance in local test plots. Similarly, the urbs model's ability to optimize energy system design was validated through sensitivity analyses and comparison with existing energy infrastructure data. We also proposed a passive cooling system using pot-in-pot refrigerators for the marketplace. The study also proposed a pilot cycle for 100 households in Diepsloot dubbed—Phezulu ‘Up’ Growers model. In addition to technical considerations, socio-economic factors such as affordability, accessibility, and community acceptance were carefully evaluated in the development of proposed interventions. Financial models were used to assess the economic viability of decentralized water, energy, and food systems, taking into account factors such as initial investment costs, operational expenses, and potential revenue streams. For more onsite models, we suggest that community engagement sessions be conducted to solicit feedback and address concerns, ensuring that proposed interventions align with the needs and aspirations of the residents in the selected settlement.

Finally, scalability and replicability of proposed interventions beyond Diepsloot were considered by identifying key success factors and potential challenges that may arise in similar informal settlements. This involved exploring adaptable strategies and flexible implementation approaches that could be tailored to meet the unique socio-economic and environmental contexts of other communities facing similar challenges.

5 Study results

5.1 Rainfall, temperature, and climate

Analysis of past rainfall, temperature, and climate trends in Diepsloot revealed that it is an ideal location for urban sack farming. Using the World Map of the Köppen-Geiger climate classification updated [28] Diepsloot has a temperate climate falling in the Cwb category (warm temperature, dry winter, warm summer). Subtropical highland climate or Monsoon-influenced temperate oceanic climate; coldest month averaging above 0 °C (32 °F) [or − 3 °C (27 °F)], all months with average temperatures below 22 °C (71.6 °F), and at least four months averaging above 10 °C (50 °F). It receives at least ten times as much rain in the wettest month of summer as in the driest month of winter (an alternative definition is 70% or more of the average annual precipitation received in the warmest six months). This means there are some months when the proposed sack farming will benefit from direct rainwater. Figure 3 shows the projected climate and temperature for Diepsloot based on the World Map of the Köppen-Geiger climate classification.

Fig. 3
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Temperature and precipitation in Diepsloot. Source: [28]

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From the climate analysis—past rainfall, temperature, and climate trends in Diepsloot, there are indications that the area is suitability for urban sack farming. Classified under the Köppen-Geiger Cwb category, Diepsloot experiences warm temperatures, dry winters, and wet summers, making it conducive to year-round cultivation. With precipitation levels significantly higher in summer, there are ample opportunities for rainwater harvesting to support crop growth, highlighting the potential for sustained agricultural production and food security in the area.

5.2 Water sources

The proposed water sources for the sack farming model in Diepsloot include groundwater and direct precipitation, which averages 740 mm per annum. These sources were selected based on their reliability and accessibility. Groundwater provides a consistent and dependable water supply, while direct precipitation offers a renewable source of water that can be captured through rainwater harvesting systems. Given the increasing water scarcity in densely populated settlements like Diepsloot, rainwater harvesting systems play a crucial role in supplementing water supply during dry seasons and reducing the strain on municipal systems. Additionally, the proposed rainwater harvesting system, which utilizes simple infrastructure such as pipes connected to rain gutters and tanks, ensures affordability and accessibility for the low-income community, addressing socio-economic disparities in water access.

5.3 Modelling of water demand and supply

We used the modelling tool AquaCrop to identify the water requirements of the various crops we proposed for Diepsloot sack farming at different stages of their development. Those requirements were compared to the availability of water through rainwater harvesting using the average roof size of households in the informal settlement of Diepsloot. The result was that even in the drier months (August, September, and October) of the vegetation period, enough irrigation water could be supplied. Figure 4 shows water demand and supply modelling with the modelling tool, AquaCrop.

Fig. 4
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Source: Authors

Modelling of Water Demand and Supply with AquaCrop.

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Assuming the sowing date is 1 August, 1 September, or 1 October, our model shows that there will be enough water for irrigation for each household. The roof water harvest per household on an average roof in Diepsloot (8m2) is projected at 3163.2 mm, 3678.4 mm, and 4035.2 mm for August, September, and October, respectively. The simulated irrigation water requirement (90% irrigation efficiency) can easily be catered at 1509.7 mm, 1480.7 mm, and 1432.5 for August, September, and October, respectively. Table 1 below shows the projected irrigation water demand and supply per household in Diepsloot—Rainfall [mm] Simulated water requirement (90% irrigation efficiency) [mm] and roof water harvest (8 m2) [mm]. The surplus water indicated in Table 1 represents the difference between the projected irrigation water supply and the simulated water requirement for farming activities per household in Diepsloot. It signifies an excess of water available beyond what is needed for irrigation, indicating favorable conditions for sustainable farming practices. This surplus water can be utilized to enhance farming sustainability in several ways. Firstly, it provides a buffer against fluctuations in rainfall patterns and ensures consistent water availability throughout the growing season, reducing the risk of crop failure due to water shortages. Additionally, surplus water can be stored and utilized for supplemental irrigation during periods of drought or high-water demand, further optimizing crop yields and ensuring food security for households in Diepsloot.

Table 1 Projected irrigation water demand and supply per household in Diepsloot.
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The AquaCrop model is widely recognized for its reliability in estimating crop water requirements and simulating crop growth under different environmental conditions. Its ability to account for factors such as soil properties, climate data, and crop-specific parameters enhances its accuracy in predicting water demand and supply dynamics. However, like any modeling tool, AquaCrop operates under certain assumptions and has inherent limitations that should be acknowledged. One key assumption of AquaCrop is that crops are grown under optimal agronomic conditions, which may not always reflect real-world scenarios. Additionally, the model assumes uniform soil moisture distribution and does not account for variations in soil texture or structure within a field, which can affect water infiltration and root water uptake. Furthermore, AquaCrop relies on simplified representations of crop physiology and growth processes, which may not capture the full complexity of plant responses to water stress or other environmental factors.

Despite these limitations, AquaCrop remains a valuable tool for water management and agricultural planning, providing valuable insights into crop water requirements and informing decision-making processes. It is important for users to interpret model outputs with caution and consider the potential uncertainties associated with the assumptions and simplifications inherent in the model. Validation against empirical data and sensitivity analyses can help assess the reliability and robustness of AquaCrop simulations, ensuring more accurate predictions of water demand and supply dynamics in agricultural systems like the sack farming model proposed for Diepsloot.

5.4 Sack farming model for Diepsloot community

Our model proposed sack farming to cater to food security among the residents of Diepsloot. Sack farming involves growing crops in soil-filled sacks, polythene bags, containers, or plastics [29]. It involves filling bags with soil, manure, and pebbles for drainage and growing plants on the top and in holes in the sides. The sacks allow people to grow food in places with limited access to arable land and water, like Diepsloot. Crops like tomatoes, onions, cabbages, pepper, mushrooms, vegetables, and many more, blossom with this method. The sack method allows a freer flow of water to the roots and retains moisture more efficiently than traditional methods, meaning sack farmers can keep their plants hydrated with less water [29]. We adapted the model that was initiated by Solidarities International in Kibera, Kenya. Kibera is East Africa’s largest slum, with approximately 250,000 people occupying about 2.5 square kilometres, making it one of the world’s most densely populated urban settlements [30]. Food is a major expense for most households in the slums of Kibera. Farmers and nonfarmers spend 50–75% of their total income on food, making sack gardening a strategic livelihood strategy [31]. Households in Kibera slums grew a combination of four crops in their sack gardens: kale (Brassica oleracea); Swiss chard (Beta vulgaris), known locally as “spinach”; green onions (Allium wakige); and coriander (Coriandrum sativum) [31].

Based on climate, rainfall, temperature, and soil analysis in Diepsloot, we proposed planting tomato, basil, spinach, and lettuce plants. The proposed and adapted stages of sowing for our Diepsloot model are:—sowing of seedlings in nurseries, preparation of the sacks by placing a stone layer at the bottom, filling the middle tube with stones (to drain the excess water), and sack with soil and manure, piercing holes and water thoroughly. Once the sacks are prepared, the plant seedlings are removed from the nursery and pressed into the soil at the top and sides of the bags. When they germinate, the shoots find their way through the holes drilled in the sides of the sacks on their way to the sun. Figure 5 shows the proposed sack farming model for Diepsloot, adapted from the Solidarities international annex handbook.

Fig. 5
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Source: Authors

Proposed sack Farming model—Sacks A–Z.

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The practical implementation of the sack farming model in Diepsloot involved adapting the method to cater to the unique conditions of the community. Comparing the proposed Diepsloot model with the one in Kibera highlights the adaptability and scalability of sack farming as a sustainable solution for addressing food insecurity in informal settlements. While specific crop choices varied between the Kibera model and our model based on local conditions, the basic principles and practices remain consistent, demonstrating the potential for replicating successful models across different regions facing similar challenges.

5.5 Spatial plant arrangements

We proposed the spatial plant arrangements (Fig. 6) for selected crops for sack farming in Diepsloot—Tomato, Basil, Spinach, and Lettuce plants. On 4.6 m2 created on the surface of a 1m2 sack, a family can grow 24 kg tomatoes (8 plants à 3 kg harvest), 80 lettuce heads, 140 spinach plants, and vast amounts of basil. With this method, about three-quarters of agricultural land can be saved. Figure 6 shows the proposed spatial plant arrangement for Spinach, Tomato, Basil, and Lettuce Plants for Diepsloot.

Fig. 6
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Source: Authors

Spatial plant arrangement.

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We modelled the spatial planting schedule for the four proposed crops (Spinach Plant, Tomato plant, Basil plants, and Lettuce Plant, based on the months they perform best, leaving the months they do not perform well, fallow; and emphasising rotation of the four crops. Figure 7 shows the planting schedule for Spinach. Starting in August, spinach will occupy fewer spots (20–30), rising to (40–50) in September and peaking at an average of 70 spots in October, November, December, and January when the conditions are projected to be more favourable for the flourishing of the spinach plants.

Fig. 7
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Source: Authors

Planting schedule for Spinach.

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5.6 Phezulu ‘up’ pilot project and market place

We proposed a community project and marketplace and named it Phezulu, meaning Up. This will be located at the central place of the selected households for the pilot project in Diepsloot. The thinking was that the proposed decentralised Water-Energy-Food system would ‘bring up’ the low-income households in Diepsloot. The vision of Phezulu ‘Up’ Pilot Project is to promote shared community space, enhance the aesthetic value of the place, create a socio-cultural meeting place, promote local economy, encourage a healthy diet, and a liveable community (Fig. 8).

Fig. 8
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Source: Authors

Phezulu ‘Up’ Pilot Project Vision.

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The proposed community centre or marketplace would be a place of inspiration and demonstration for decentralised Water-Energy-Food systems. The centre will be an exemplary space for training and research purposes in cooperation with on-site NGOs like Dell Learning Lab and research. It will also be a place for productive community socialisation, distribution of resources (for example, sacks) to project participants, and selling of excess vegetables to other community members in Diepsloot. The market booth will also be used as a storage place for gardening utensils, soil, and seeds and refrigeration of vegetables using a pot-in-pot refrigerator system. The marketplace will also be powered by solar energy on the roof of the marketplace, and it will also be a temporary living space for selected project personnel. Ultimately, the proposed community centre or marketplace will contribute to place-making. Place-making focuses on inspiring and encouraging communities to create their own space/ places where they feel they have a strong stake and can commit to improving things [32]. Communities collectively shape their public realm through place-making to maximise shared value [33]. The focus on place-making reminds urban planners of the human aspect of city-building. The ultimate goal is to create places people use, inspire social interaction, and promote community stewardship. In the African context, particularly in South Africa, the concept of place-making is yet to be adopted or incorporated in the context of slums/informal settlements plans and upgradation techniques.

The selection of a marketplace as the central point for the Phezulu ‘Up’ pilot project in Diepsloot, is based on several considerations. Firstly, it serves as a strategic location accessible to the selected households participating in the project, facilitating community engagement and involvement. By positioning the decentralised Water-Energy-Food system at the heart of the community, it aims to uplift low-income households in Diepsloot by providing essential resources and fostering socio-economic development. The marketplace concept also aligns with the vision of promoting shared community space, enhancing the aesthetic value of the area, and creating a socio-cultural meeting place. Additionally, the marketplace offers opportunities for promoting a localised economy, encouraging healthy dietary practices, and fostering a liveable community environment. Moreover, it serves as an exemplary space for training, research, and collaboration with on-site NGOs, facilitating knowledge transfer and capacity building within the community.

Furthermore, evidence supports the effectiveness of decentralised Water-Energy-Food systems in uplifting low-income households. These systems promote sustainable resource management, enhance food security, and improve access to clean water and energy. Studies have shown that implementing decentralized solutions tailored to the specific needs of low-income communities can lead to significant socio-economic benefits. For example, rural electrification projects in sub-Saharan Africa have demonstrated the techno-economic advantages of decentralised energy systems. Similarly, initiatives promoting rainwater harvesting and sustainable agriculture have shown promising results in enhancing water and food security in informal settlements.

5.7 Energy requirements at the market centre

Besides solar energy that will power the marketplace, we proposed a passive cooling system using pot-in-pot refrigerators (Fig. 9) to keep vegetables fresh in an environmentally friendly way is proposed. A pot-in-pot refrigerator, clay pot cooler, or zeer (Arabic) is an evaporative cooling refrigeration device that does not use electricity [34]. A zeer is constructed by placing a clay pot within a larger clay pot with wet sand in between the pots and a wet cloth on top [35]. The device cools as the water evaporates, allowing refrigeration in a hot, dry climate. It must be placed in a dry, ventilated space for the water to evaporate effectively toward the outside. It uses a porous outer clay pot (lined with wet sand) containing an inner pot (which can be glazed to prevent penetration by the liquid) within which the food is placed. The evaporation of the outer liquid draws heat from the inner pot. The device can cool any substance and requires only a flow of relatively dry air and a source of water [36]. In training sessions, members can learn how also to build pot-in-pot refrigerators for their homes.

Fig. 9
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Source: [36]

Pot-in-pot-refrigerators.

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To supply the marketplace with electricity, PV panels will be installed on the roof of the booth. The pilot project envisages establishing partnerships with existing initiatives to promote PV installations and facilitate the training of local technicians. Figure 10 below shows the energy demand curve for the marketplace projected by urbs with a peak demand of over 80 Watts expected during the day between 7 am and 6.00 pm, and the least demand of just above 20 Watts that will be used only for lighting at night.

Fig. 10
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Source: Authors

Energy demand curve for the marketplace projected by urbs.

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5.8 Phezulu ‘up’ growers model

We proposed a growers’ model for Phezulu pilot project in Diepsloot. The model envisages providing urban agriculture and rainwater harvesting training for growers, a grower’s kit for 2 sacks per household (100 households), and ongoing support for growers through community mobilisers and mobile planning tool and providing a market area for growers. Targeting 100 randomly selected households on one of the clusters in Dieploot, the potential distribution of project members or sacks for the pilot project is shown in Fig. 11.

Fig. 11
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Source: Google Earth

Potential Distribution of Households or Sacks.

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Through crowdfunding, partnerships with governmental agencies and the city of Johannesburg, and a monthly subscription fee of 60 ZAR, we propose the supply of two sacks per household, ad hoc training and support, and access to a nursery within the marketplace. A pessimistic cost analysis of the 2-year pilot cycle results in a return on investment of $800, which can be used in subsequent cycles. The cost analysis per sack as shown on Fig. 12 is: seeds (34 ZAR), sack (65 ZAR), soil (228 ZAR), compost (251 ZAR), and PVC (15 ZAR), all amounting to a total of 578 ZAR.

Fig. 12
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Source: Authors

Cost analysis per sack.

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The Phezulu ‘Up’ Growers Model proposed for the pilot project in Diepsloot faces potential risks and challenges that need to be addressed to ensure its success and sustainability. One significant concern is the issue of equity and inclusivity within the community. Given the socio-economic disparities present in informal settlements like Diepsloot, it is essential to ensure that all community members, especially marginalized groups, have equal access to project resources and opportunities. To address this, the project will implement targeted outreach and engagement strategies to reach vulnerable households, prioritize their participation, and provide tailored support to meet their specific needs. Additionally, the project will establish transparent decision-making processes and mechanisms for community input to ensure that all voices are heard and represented in project planning and implementation.

Another challenge is the integration of local knowledge and practices into the project design. While external expertise and technical solutions play a crucial role, it is equally important to leverage the knowledge and skills of community members to ensure project relevance and sustainability. The project will actively involve community members in co-designing and co-implementing activities, drawing on their traditional knowledge of farming practices, local environmental conditions, and cultural preferences. Through integrating local knowledge and practices, the project can build trust and ownership within the community, leading to more effective and sustainable outcomes. To mitigate potential risks and challenges, the project will adopt a comprehensive risk management strategy. This strategy will include regular monitoring and evaluation of project activities to identify emerging issues promptly, proactive communication with stakeholders to address concerns and build consensus, and flexibility in project design to adapt to changing circumstances. Additionally, capacity-building activities will be conducted to empower community members with the skills and knowledge needed to overcome challenges independently.

5.9 Cost analysis and funding of the pilot project

The pilot project’s cost analysis shows an initial investment requirement of $USD15 263 USD. This includes purchasing immovable assets of approximately $USD5, 742, and outgoing costs (first cycle) of $USD8 885. Immovable assets include equipment purchases for and infrastructure development necessary for setting up the project, while outgoing costs cover operational expenses such as labor, utilities, and maintenance. The incoming revenue for the first cycle is projected at $USD9 629 with a projected return on investment of $803 per cycle. The projected incoming revenue is based on a comprehensive market analysis and pricing strategy. Factors considered include the demand for fresh produce in the local community, prevailing market prices for similar products, and the purchasing power of target customers. Assumptions made include the adoption rate of the pilot project by households in Diepsloot and the average spending per customer. The pricing strategy aims to strike a balance between affordability for low-income households and profitability for sustaining the project. The projected ROI of $803 USD per cycle indicates the potential profitability of the pilot project. This ROI is crucial for assessing the financial sustainability and success of the initiative. Comparing this ROI with industry standards or similar projects provides valuable insights into the project's performance and competitiveness. Additionally, the ROI serves as a key metric for attracting potential investors and securing future funding for project expansion. Several risks may impact the projected ROI, including fluctuations in market demand, competition from existing suppliers, regulatory challenges related to land use or permits, and operational risks such as supply chain disruptions or crop failures. These risks were considered in the cost analysis by incorporating contingency measures and buffer funds to mitigate their impact on financial outcomes. Continuous monitoring and proactive risk management strategies will be employed to address emerging challenges and optimize the project's profitability over time.

The proposed funding sources for Phezulu pilot project are crowdfunding (monthly community subscriptions), government agencies, including the City of Johannesburg, and international organisations. After presenting the feasibility and potential benefits of the project to the local communities in Diepsloot, we anticipate positive support from these key stakeholders.

6 Conclusion and future directions

In conclusion, our study demonstrates the significance of decentralized Water-Energy-Food systems in addressing the complex challenges of water, energy, and food security in marginalized urban environments like Diepsloot, Johannesburg. Employing space analysis, least-cost modeling of sack farming, and integrating renewable energy technologies, we provided actionable solutions tailored to the specific needs of Diepsloot community. Our hypothesis, predicting that the implementation of decentralized WEF systems would enhance resource access, socio-economic development, and environmental sustainability, has been validated through our findings. The suitability of Diepsloot for urban farming, coupled with proposed water sources and spatial plant arrangements, demonstrates the potential for sustainable agriculture even the area being a densely populated informal settlement. The proposed Phezulu ‘Up’ Growers model, along with crowdfunding and governmental support, presents a promising avenue for empowering local communities and fostering economic resilience. Our study not only contributes to the academic discourse on WEF systems but also provides practical insights for policymakers, urban planners, and community stakeholders.

Our findings corroborate with other recent studies done on Water-Energy-Food Systems [2, 4, 14] also demonstrating how decentralised Water-Energy-Food integrated models can be an alternative and innovative approach to achieving SDGs, in particular SDG 2 (zero hunger), SDG 6 (clean water and sanitation), and SDG 7 (affordable and clean energy) [37]. We also draw key learning points from our study. First, urban agriculture through sack farming can be a viable and important livelihood strategy for households in densely populated slum environments. Urban gardening contributes to the SDGs by decreasing poverty, preventing hunger, improving health and well-being, promoting decent work and economic growth, creating stronger communities, making production and consumption more responsible, reducing carbon emissions, and improving biodiversity. Thus, low-space urban agricultural activities like sack gardening should receive greater consideration as part of urban planning and development initiatives. The Water-Energy-Food nexus approach can also contribute to community place-making—creating community cohesion and a feeling of belonging for an otherwise disregarded faction of society.

Looking ahead, it is crucial to continue engaging with local communities and leveraging partnerships with governmental agencies to ensure the successful implementation of decentralized WEF systems. Moreover, ongoing monitoring and evaluation will be essential to assess the long-term impact of our interventions and refine our approach based on real-world feedback. Ultimately, our study serves as a blueprint for addressing water, energy, and food security challenges in marginalized urban areas, paving the way for inclusive and sustainable development that prioritizes the well-being of all residents. While our findings demonstrate the feasibility and potential benefits of decentralized Water-Energy-Food systems, critical considerations must be addressed for successful implementation. These include a robust critique of the practical implementation of sack farming, comparative analysis with other models in other regions like Kibera, Kenya, justification for chosen project components such as the marketplace and community centers, discussions on the effectiveness of decentralized WEF systems in uplifting low-income households, identification and mitigation of potential risks and challenges, strategies for ensuring equity and inclusivity within the community, and the integration of local knowledge and practices into project design. Lastly, the planning and implementation of decentralised WEF systems in marginalised urban communities should take into account factors like the adoption of appropriate technology, future economics of scale, local socio-economics, and local governance rules, household ability to pay for subscriptions, government subsidies, and potential for international donations [3].