**4. Current sanitation backlog and bottlenecks**

Providing sanitation services to a city as a whole invariably requires a mixture of sanitation systems, which are appropriate for different parts of the city and which can be implemented at different scales [5]. It is unlikely that the same model of service delivery will be appropriate for all areas. Therefore, a citywide sanitation plan is likely to consist of several components designed to meet the specific physical, socio‐economic and service conditions for different parts of the city. The city is characterised into sanitation zones or clusters based on such aspects as topography, population density, user preferences, affordability, existing systems and/or water availability, taking into account both the existing situation and expected changes due to urbanisation. This helps to determine where on‐site or off‐site, networked or non‐networked,

The previous section highlights urban diversity and the related heterogeneity in terms of sanitation status. Different contexts mean different sanitation systems, therefore it is important to adopt a sanitation system approach, as illustrated by [6]. Sanitation cannot be reduced to latrines or sewers but needs to be considered as a whole value chain, consisting of a user interface (the toilet), collection/storage (e.g. pits and septic tanks), conveyance (e.g. sewers or vacuum trucks), treatment and use and/or disposal. In particular, systems can be categorised as sewered or non‐sewered, as well as dry or wet (without or with water). They can also be differentiated through their scale/domain of application: on‐site (for households or buildings), small‐scale (for cluster of houses or neighbourhoods) or large‐scale (centralised at city level). Urban centres and western cities are usually served by a single‐sewer network that conveys the wastewater to a treatment plant; we will refer to this type of system in this chapter as the 'conventional system'. However, most cities around the world still rely mainly on on‐site systems, where domestic wastewater accumulates in pits and tanks in a form called 'faecal sludge' or 'septage'. Now and then, this faecal sludge needs to be pumped and transported to

It is clear that it will not be possible to connect all urban areas to a conventional system in the foreseeable future. Nor is it desirable. The main bottleneck is of course financial: the amount of money needed to provide this is immense, and most governments do not have enough funds to build such infrastructure; besides, when such an infrastructure exists, the risk of failure is high when there is no financial means and capacities to operate and maintain the system properly. The further one is from the city centre, the more expensive it also gets. The economies of scale that can be achieved at the treatment plant level are outweighed by the dis‐economies of scale of the sewer network [7]. Low‐density peri‐urban areas especially have a very high cost per capita. Sometimes, the geography and population density of the city make a conven‐ tional system simply unrealistic, such as in Durban, South Africa, which is characterised by low density and a hilly topography. Other cities such as Dakar, Senegal, fully assume faecal sludge management (FSM) as part of its sanitation system in its own right, cohabiting with sewers. By accepting this and by investing in FSM, the utility ends up treating a lesser volume of wastewater per capita, while avoiding the massive investments required to provide a sewer

dry or wet systems are most appropriate in the short‐ and long term.

**3. Sewered or non‐sewered: various sanitation systems**

a faecal sludge treatment plant.

118 Sustainable Urbanization

While development priorities shift from the millennium development goals (MDGs) to the sustainable development goals (SDGs), it has to be recognised that few low‐ and middle‐ income countries were even close to reaching their sanitation MDGs. In many of them, demographic growth outweighed the progress made, despite the billions of dollars poured into the sector. A lot of infrastructure is not adapted to the context and/or not sustainable, thus failing to serve the population properly in the long run. Besides, the conventional approaches fail to reach large (and often most) parts of the population. The dearth of pragmatic answers to the need for quick increases in sanitation coverage is mainly due to the lack of an enabling environment to develop solutions that move away from the conventional system. Lüthi et al. [9] structure the enabling environment in six categories: (i) government support; (ii) legal and regulatory framework; (iii) institutional arrangements; (iv) skills and capacity; (v) financial arrangements; and (vi) socio‐cultural acceptance. In the past, many water and sanitation projects failed because of the lack of an integrated approach. Sanitation programmes should take these six dimensions into consideration to ensure the long‐term sustainability of sanitation infrastructure and services.

The major barriers to progress in sanitation coverage lie within the institutions, policies and realities of low‐ and middle‐income countries [2]. The public sector is often weak in terms of skills, structures, planning capacity and bureaucratic procedures, and mechanisms are not always in place to recover investment, operation or management costs, leading to the degra‐ dation of service provision or even system failure. Depending on the political structure of the city, the division of responsibilities relating to sanitation can be an institutional headache. Responsibilities for sanitation service provision are often fragmented and sometimes overlap‐ ping among different departments and ministries. This fragmentation and overall 'poor' urban governance make coordinated action difficult and can even lead to conflict between stake‐ holders for resources and areas of influence.

For example, some reasons why faecal sludge management systems have not been widely implemented are the financial and political complexity involved, as well as the overlap‐ ping and unclear allocation of responsibilities and a lack of incentives for efficient opera‐ tion [10, 11]. This is due to the number of stakeholders who have a financial interest in the system and also to the diversity of interests of each stakeholder. Unlike other types of infrastructure (e.g. electricity) where a single utility is usually responsible for generation, delivery, operation, maintenance and billing, a faecal sludge system is more commonly a collection of stakeholders, each of whom is responsible for a different part of the treat‐ ment chain. Dysfunctional institutional frameworks result in both a lack of accountability and disagreements between stakeholders, which can even sometimes lead to sector block‐ age.

The situation is similar with small‐scale and on‐site systems: such systems often show a mis‐ match with many institutional conditions (regulations, professional codes or user expecta‐ tions) [12]. Many factors have been put forward to explain that conventional sewerage remains the predominant paradigm for urban sanitation delivery. There is, however, little hard evidence to say whether this is mostly due to bureaucratic or technical inertia, risk aversion, corruption (and, hence, the preference for high‐cost schemes with limited local ac‐ countability), political expediency (the need to be seen to be doing something), the percep‐ tion that only these systems are 'modern', or simply a lack of knowledge [13]. What is clear is that whatever incentives currently exist tend to encourage local and central authorities and their advisors to stick to conventional top‐down planning and conventional centralised sewerage schemes.

Moving beyond conventional approaches towards sustainable urbanisation needs to be both top‐down and bottom‐up. Top‐down, because it is often the only way to reform institutions, laws and regulations and bottom‐up, because little can be done without dynamic individuals, communities and private sector stakeholders who have the energy, vision and creativity to innovate and validate new approaches. Flexibility is needed from governments to integrate non‐governmental initiatives in their planning and to allow them to be replicated and scaled up. Above all, developing the right incentives to let initiatives grow and prevent them from being stopped by the established bureaucracy is essential.
