Uncomfortable truths: How Shit Flow Diagrams expose the gaps in urban sanitation systems – and help to close them
In rapidly growing cities in Africa and Asia, the sanitation needs of the very poorest are often neglected – to the detriment of public health. By visualising how excreta is managed as it moves through a city, Shit Flow Diagrams can help municipal authorities to prioritise investments where they are needed most.
A novel diagram upends a long-standing orthodoxy
Looking back, one can almost pinpoint the moment when the urban sanitation orthodoxy in Lusaka, Zambia began to falter. It involved a diagram, compact enough to fit on a single sheet of paper, featuring roughly a dozen red and green lines of varying thickness which snaked their way across the page.
The year was 2015, and the diagram was a visualisation of excreta flows, colloquially known as a Shit Flow Diagram (SFD). This radically simple tool, developed a few years earlier by a team of water and sanitation experts at the World Bank, was instrumental in convincing key decision-makers at international financial institutions, as well as at the Lusaka Water and Sewerage Company, to widen the focus of a major new sanitation program beyond flush toilets, sewer pipes and wastewater treatment plants.
At a critical moment, the SFD helped them see that it would be impossible to make significant improvements in Lusaka’s sanitation situation without addressing ‘the elephant in the room’ – the unsafe management of faecal sludge, the mix of faeces, urine, water and other solid waste that accumulates in the pits, tanks or vaults of sanitation facilities that are not connected to sewers.
Why this was the case – and how the SFD helped to make this clear – is the subject of this article. It tells the story of a surprisingly effective tool whose application – with support from German development cooperation and other partners – in more than 160 cities worldwide is helping to focus attention and trigger action on the most neglected aspect of urban sanitation.
A global fixation on sewers hampers progress on urban sanitation
According to the WHO/UNICEF Joint Monitoring Programme for Water Supply, Sanitation and Hygiene (JMP), 46% of people living in urban areas – some 1.9 billion people worldwide – do not have access to safely managed sanitation services. While this marks an improvement over five years ago, when 53% lacked such access, the rate of progress still falls short of what is required to meet the targets for adequate and equitable sanitation set out in Sustainable Development Goal 6.2.
One reason for this is the rapid pace of urbanisation, but another is that favored approaches for improving urban sanitation have disproportionately benefitted the better-off. For half a century, the conventional wisdom in the sanitation sector has seen flush toilets linked to sewers as the ‘gold standard’, regardless of a city’s level of economic development. However these ‘off-site’ sanitation systems (referred to as such because excreta is not contained, but immediately transported through pipes to a separate location for treatment and disposal) are only accessible to a very a small proportion of urban residents. Only 16% of urban dwellers in Sub-Saharan Africa use sewered sanitation; in Central and Southern Asia, the figure is slightly higher, at 38%.
In most low- and lower-middle income countries, the sewers operated by utility companies date back to colonial times, when they were constructed to serve certain privileged areas in city centers. In the post-colonial period, government ministries, municipal authorities, utility companies and international financing institutions have built incrementally upon these existing systems, laying new pipes to reach more households with sewer connections. Rarely, however, have these connections extended into poorer neighborhoods, to say nothing of unplanned, overcrowded settlements on urban peripheries which often lack piped water and other municipal services. The fixation on sewers has hindered the development of inclusive, citywide sanitation systems which serve the needs of all residents.
The invisible majority and the challenge of faecal sludge management
If utilities are responsible for providing sanitation services to customers with sewer connections, who is responsible for everyone else? The short answer is: no one. In most places, people who live in areas where there are no sewers have largely been left to their own devices to come up with ‘on-site’ sanitation solutions.
‘Toilets that are not connected to the sewer have long been invisible as far as the sanitation sector is concerned,’ says Dr Arne Panesar, from the program ‘Water Policy – Innovations for Resilience’ implemented by the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH on behalf of the German Federal Ministry for Economic Cooperation and Development (BMZ). ‘This means that the people who use them are also invisible. They fall outside what the sector sees.’
On-site sanitation systems vary widely in terms of the standards to which they are constructed and the extent to which they prevent unsafe exposures of excreta into the environment, including into open drains and groundwater. The most common types are underground septic tanks, into which household wastewater is flushed, and lined or unlined pit latrines which are dug into the earth.
The faecal sludge which accumulates in these tanks and pits needs to be managed safely to avoid public health threats, such as cholera and typhoid. Yet professional faecal sludge management services – including emptying, transport and treatment – are generally lacking. Households that wish to have their tanks or pits emptied can turn to private companies and informal emptying services, but what actually happens to emptied faecal sludge is a major concern. Illegal dumping is widespread. In its most recent report, the Joint Monitoring Programme notes the need for stronger systems for monitoring the safe management of faecal sludge, and for investments in formal services for emptying, removal and treatment.
SFDs create a language for talking about citywide sanitation
Given this diversity of arrangements, it is not surprising that in many cities no one holds an overview of the sanitation landscape. In the ‘on-site’ sanitation corner are a bevy of NGOs, community water trusts, operators of faecal sludge treatment plants, septic tank builders, tanker truck operators, and informal workers who dig and empty pit latrines. In the ‘off-site’ sanitation corner are the utility companies, water engineers and wastewater treatment operators who make the sewer system run.
Although all these stakeholders are part of the same sanitation ecosystem, it doesn’t always feel this way. They embody two different schools of thought – which is reflected in their use of terminology, the technical expertise they bring to the table, and the way in which they understand the urban sanitation challenge.
The revolutionary contribution of the SFD comes in bringing all these different strands together. It visualises in a single drawing what happens to excreta across an entire city – through off-site sanitation systems as well as on-site ones. Tracing the movement of faecal matter along the ‘sanitation chain’ – containment, emptying, transport, treatment and re-use/disposal – it shows the portion of a city’s overall excreta that is safely managed and the points at which faecal pollution occurs. In doing so, it makes visible the parts of the urban sanitation system which have long been invisible.
Because the SFD is comprehensive, everyone – from the faecal sludge management advocate to the wastewater engineer – can find themselves in the diagram and can understand how their work fits into the bigger picture. The diagrams are simple enough that non-sanitation experts can grasp them, too. This is crucial in creating a shared understanding and a common language to talk about the city’s sanitation challenge, where the main problems lie, and what it will take to reach an inclusive, integrated, citywide sanitation system.
In Lusaka, an SFD unlocks investment for formal, on-site sanitation services
This is exactly what has begun to happen in Lusaka.
Lusaka’s first SFD caught people’s attention: it showed that 75% of the excreta produced in the city was not being safely managed. By far the greatest problem was the handling of faecal sludge from pit latrines, the predominant type of on-site sanitation facility in the large peri-urban areas in which 70 percent of Lusaka’s 1.5 million people live.
This uncomfortable truth landed at the right moment, just as key decisions were being made about the shape of the 240 million Euro Lusaka Sanitation Program, a multi-year investment program financed by the World Bank, the African Development Bank, the European Investment Bank and Germany’s KfW Development Bank and implemented by the Lusaka Water and Sewerage Company.
Following intense discussion, a decision was taken to allocate a small portion of the financing for the development and roll-out of on-site sanitation services in selected peri-urban areas. While the bulk of the program still focused on laying new sewer pipes and improving wastewater treatment capacity, the Lusaka Water and Sewerage Company would also be responsible for building thousands of emptiable toilets for customers in peri-urban areas, constructing a new faecal sludge treatment plant, and contracting with private companies to provide emptying services for pit latrines and septic tanks.
Although the company had been testing out service models on a pilot basis, this marked the first attempt to provide on-site sanitation services at scale and to develop a business model, linked to a tariff structure, which would allow them to eventually be sustained.
SFDs help the Lusaka Water and Sewerage Company prioritise where to intervene…
Over the past five years, as the Lusaka Water and Sewerage Company set out to do just this, several more SFDs have been developed in Lusaka and used to steer decisions about interventions and investments. Mwansa Nachula Mukuka, who leads the on-site sanitation component of the Lusaka Sanitation Program for the company, is positive about the tool. ‘SFDs add value, especially in terms of planning,’ she says. ‘When you have limited resources to work with, you need to prioritise where to intervene.’
According to Nachula Mukuka, the initial diagram helped the utility decide to focus its efforts on Kanyama and George compound, two peri-urban areas that are particularly cholera prone due to the high proportion of untreated faecal sludge and the vulnerability of the groundwater.
Then, a few years later, when the company had researched delivery models and was ready to plan its interventions for these two areas in detail, the GIZ-implemented Climate-Friendly Sanitation Services in Peri-Urban Areas of Lusaka (CFS-Lusaka) project supported it to prepare neighborhood-level SFDs based on data from a house-to-house mapping of sanitation facilities.
This helped the utility to better target its activities and provided a solid baseline from which to measure progress. Next year, the company intends to prepare new SFDs to see what the investments have meant in terms of the proportion of safely managed faecal sludge.
… and catalyse relationships between the utility and municipal authorities
Trevor Surridge, who led the CFS-Lusaka project on behalf of GIZ, found that these neighborhood-level SFDs helped to strengthen cooperation between key stakeholders at the utility and the city council who were essential for the successful establishment and roll-out of on-site sanitation services. ‘We’d all seen the data, but when this was translated into a visual, it had a different effect,’ he says. ‘It showed that if we don’t work together, we’ll never solve this picture. The SFDs helped to catalyse those relationships.’
Over a period of several years, the project repeatedly brought together the same core group of managers, health inspectors, technical engineers and other staff from the city council and the utility at various meetings and events. Gradually, the linkages became more robust and the success of on-site sanitation turned into a shared goal. This could be seen, for example, in the development of a new municipal by-law about the design of emptiable latrines.
‘If you think about citywide inclusive sanitation, Lusaka is actually walking the talk,’ says Mwansa Nachula Mukuka. ‘Over the last five years, we’ve reached the point where the regulator, the local authority and the utility are all moving in the same direction, and each stakeholder is trying to fulfil its responsibility so that the others can do their part.’
‘It’s been an exciting journey,’ she adds. ‘If we continue at this pace, Lusaka can become a model for citywide sanitation.’
By communicating the challenge, SFDs can help to change the sanitation narrative
Six years after that first SFD, Lusaka now boasts nearly 5000 new emptiable toilets in two of the city’s poorest areas. Professional sanitation workers provide toilet and septic tank emptying services, safely removing sludge and transporting it to faecal sludge treatment plants for treatment and disposal.
In 2019, the Lusaka Water and Sewerage Company became the Lusaka Water Supply and Sanitation Company, a name which reflects its responsibility for all city residents, not only those with sewer connections. A fully-staffed Faecal Sludge Management Unit leads this growing area of work.
Water and sanitation companies in six other Zambian cities are in the midst of preparing SFDs with support from the GIZ-implemented Reform of the Water Sector Program. They intend to use these as a starting point for the development of their own on-site sanitation services, something which is now required by NWASCO, Zambia’s regulatory agency for water supply and sanitation.
‘As long as cities are trying to change their sanitation narratives, they require tools like SFDs to communicate and point out problems,’ says Chaiwe Sanderse, a consultant with the African Development Bank Group and former advisor with the CFS-Lusaka project. ‘I can’t imagine a scenario where cities can set out to change things without something like this.’
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