Does "Low Cost" Urban Sanitation Exist? Lessons from a Global Data Set

Abstract

In this paper, we report results from, and demonstrate the value of, a global database for the collection and aggregation of reliable and comparable cost data for urban sanitation systems as they are built and operated on the ground (rather than the "as planned" costs that are often reported). We show that no particular "mode" of urban sanitation (for example "sewered sanitation" or "fecal sludge management") can be meaningfully described as "low cost" when compared to other modes. We show that economies of scale may operate for systems that transport waste from pits and sealed tanks by road as well as for sewerage. We use a case study example to show the value of being able to compare local costs to global benchmarks and identify that operational considerations such as low connection rates may be more significant in determining overall cost liabilities for urban sanitation than technical considerations such as population density, size, and degree of centralization/decentralization.

Keywords: benchmarking; cost; costing standards; sanitation; urban.

Figure 1

Distribution of summed total annualized cost liability [Int$ (2020)] for synthetic archetypal urban sanitation systems, based on 125 data points collected by the CACTUS project as of June 2023. The horizontal bar shows the median cost for each system. Sealed tanks without infiltration which are regularly emptied can be used to manage both black and gray water safely while pits and tanks with infiltration cannot and will therefore be unsuitable in most urban places. All sewers carry domestic gray water along with blackwater; combined sewers also carry stormwater. Equivalent cost effectiveness cannot therefore be inferred across all systems based on costs alone.

Figure 2

Total annualized cost liability [Int$ (2020)] for containers and emptying/transport in urban sanitation systems with no sewerage from data collected by the CACTUS project as of June 2023. Boxes show the interquartile range, x is the mean, and the horizontal bar is the median for each component.

Figure 3

Total annualized cost liability [Int$ (2020)] for emptying and transport services from data collected by the CACTUS project as of June 2023. Best fit lines by least-squares method, after removal of outliers (quantile less than 0.95).

Figure 4

TACH [Int$ (2020)] by component for Narok town (mean values shown as star icons), compared to the CACTUS database (full data range shown excluding data from Narok) as of June 2022. Boxes show the interquartile range, x is the mean, and the horizontal bar shows the median for each component. For the sewerage (pipes-conventional, separate, no pumping) in Narok, the current value of TACH and the theoretical value of TACH assuming 100% design connectivity is achieved are both shown.

Figure 5

TACH [Int$ (2020)] for whole sanitation systems for Narok town (box plots) compared to the CACTUS database (bars), excluding the data from Narok, as of June 2022. Boxes show the interquartile range, x shows the mean, and the horizontal bar shows the median for each component.

Figure 6

Whole-system TACH [Int$ (2020)] of sewerage for Narok town plotted against sewer connectivity. The stacked bars illustrate the share of the costs associated with each element of the sanitation value chain, and the line chart shows the total cost plotted against percentage sewer connectivity. The data table shows TACH broken down by component, corresponding to the bars above.