**2. Different urban contexts—different sanitation challenges**

Cities are not homogeneous, especially in low‐ and middle‐income countries. Lüthi et al. [4] identified four typical urban contexts: (1) inner‐city middle and high‐income settlements, (2) planned urban development areas, (3) informal settlements and (4) peri‐urban interface (see **Figure 1**). Contrasts between these contexts can be striking, that is skyscrapers and slum pockets in India or favelas next to villas with swimming pools in Brazil. It is currently common to find modern city centres next to informal neighbourhoods that lack the most basic services. The tendency in current urbanisation is an increase in segregation, with a densification and sprawling of informal settlements on the one side, and the rapid extension of medium density planned urban development areas, that is large fully fledged new neighbourhoods or gated communities for the middle and upper classes, on the other.

that the global population in 2100 will be 11.2 billion. It is estimated that Africa will have 39%

The rapidly urbanising societies of Africa, Asia and Latin America are constricted by a quadruple challenge: urban environmental degradation, global climate change with accentu‐ ating water stress, infrastructure deficits and fast expanding peri‐urban areas and informal settlements. As pointed out by [2], even when urban sanitation management infrastructure is available, it often serves only a small percentage of the urban population. Small‐ and medium‐ sized towns (<500,000 inhabitants) will carry the brunt of future urbanisation in low‐ and middle‐income countries and will have a pronounced backlog in urban sanitation infrastruc‐ ture. A recent infrastructure study of the World Bank highlighted the low access to improved sanitation in urban Africa with 51% of the population relying on traditional (unimproved) latrines, 14% on improved latrines and only 25% connected to sewers or a septic tank [3].

Urban sanitation is at an inflection point. The international community and national govern‐ ments are increasingly acknowledging that conventional sewer‐based sanitation cannot be the solution for all the different urban areas. Apart from the lack of capital, there are other good objective reasons why conventional urban water management does not offer the only solution for the rapidly growing cities in Asia and Africa: the lack of stable energy supplies, of spare parts and of human resources for reliable operation are factors that limit the expansion of centralised systems. In an increasing number of cities, water scarcity is also becoming an important bottleneck. As a special case, the improvement of sanitation conditions in informal settlements in low‐ and middle‐income countries has proven difficult due to disabling institutional environments, as well as the lack of secure tenure and of the rule of law, often preventing the development of innovative management schemes. Today, a majority of urban citizens rely on on‐site systems, such as septic tanks, pit latrines or cesspits. With sewer‐based systems out of reach for a large part of the global population, there is an urgent need to develop more cost‐effective and resource‐efficient systems that can deliver the desired water services necessary for public health, protection against flooding, and the preservation of natural resources. In this chapter, we present the main reasons for environmental sanitation deficits and lay out arguments for a holistic sectoral approach that is inclusive and that incorporates

of the world's population, almost as much as is estimated for Asia [1].

116 Sustainable Urbanization

innovative management arrangements for growing urban areas.

**2. Different urban contexts—different sanitation challenges**

Cities are not homogeneous, especially in low‐ and middle‐income countries. Lüthi et al. [4] identified four typical urban contexts: (1) inner‐city middle and high‐income settlements, (2) planned urban development areas, (3) informal settlements and (4) peri‐urban interface (see **Figure 1**). Contrasts between these contexts can be striking, that is skyscrapers and slum pockets in India or favelas next to villas with swimming pools in Brazil. It is currently common to find modern city centres next to informal neighbourhoods that lack the most basic services. The tendency in current urbanisation is an increase in segregation, with a densification and sprawling of informal settlements on the one side, and the rapid extension of medium density

**Figure 1.** Main settlement contexts that need to be addressed in urban sanitation in low‐ and middle‐income countries (Source: [4], p. 79).

Inner‐city middle‐ and high‐income settlements, as well as planned urban development areas, are usually characterised as having conventional centralised water supply and sewer system schemes managed by governmental institutions, typically a utility. Informal settlements and the peri‐urban interface, however, often rely on on‐site sanitation systems, from basic pit latrines to flush toilets with septic tanks, and sometimes on water kiosks or water trucks for their water supply. These so‐called 'off‐the‐grid' solutions are often not managed by the government, but by self‐organised private stakeholders, community‐based organisations or NGOs.

The characteristics of low‐income settlements make the provision of basic services intrinsically very difficult and, therefore, conventional service delivery approaches are often not viable [5]. For instance, slums are often located in areas with specific physical constraints, such as low‐ lying ground, steep slopes or densely packed housing with very poor access via narrow and irregular pathways. When settlements are informal, key sanitation stakeholders are reluctant to invest: governmental agencies, because such area is not formal and thus not recognised; landlords, because they often do not live there; and tenants, because they are afraid of gentrification and do not want to invest without having security of tenure. This usually results in the inhabitants of such neighbourhoods paying much more for water and sanitation than people served by the government, and the services that are provided often threaten public health.

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