Estimate Capital Costs

The capital cost of a sanitation facility will vary widely, depending on, among other factors, material and labor costs, population density, soil conditions, and the type of sanitation provided. So, any overall cost figures should be treated with great caution. The table below from the WHO/UNICEF (2000) JMP Global Water Supply and Sanitation Assessment Report 2000 gives median construction costs for a range of sanitation technologies for Africa, Asia and Latin America and the Caribbean. The report states that the average construction costs for a range of sanitation facilities should be used with caution since the level of facilities associated with the indicated costs are not clear. The report notes that “while simple on-site systems tend to be cheaper than systems such as sewerage and septic tanks, the difference is sometimes less than might be expected.” See also the effect of the housing density and taking account of sunk cost, below.

Table: Per capita costs of the various sanitation options

Source: WHO/UNICEF (2000) WHO/UNICEF (2000)Global Water Supply and Sanitation Assessment Report

Even within countries, capital costs of sanitation technologies may vary from place to place, depending on ground conditions, the cost of materials and, in some cases, housing density. The variations in cost are much greater for sewered options, and are strongly influenced by housing density.

Capital costs for treatment, like all sanitation related costs, vary widely with scale, treatment requirements, waste composition, site conditions etc. One serious review of sanitation costs (Loetscher, 1999, cited in UNEP, 2000 Appendix 2) listed the following average ratios of wastewater treatment capital costs relative to those of a single family septic tank, the approximate costs of which are shown above. The author notes that these estimates are based on costs from a limited number of countries. Note that these costs would then be added to the cost of sewerage above. As with other cost data in this guide, these should only be viewed as a very approximate starting point.

Table: Capital cost relative to septic tank

Source: UNEP, 2000 (Appendix II)

Effect of Housing Density on Cost

It is logical that the per capita capital cost of both conventional and ‘simplified’ sewers drops with increased population density. For instance in Natal, northeast Brazil, the household cost of simplified sewerage reduced rapidly up to population densities of around 80 people per hectare. As the population density increased, there was a more gradual reduction in cost. Simplified sewerage became cheaper than on-site systems at a population density of around 160 people per hectare. It was concluded that the capital costs of simplified sewerage in 1980 were US$ 325 per household, compared with around US$ 1,500 per household for conventional sewerage. Similar levels of cost saving have been recorded elsewhere, such as Orangi Pilot Project in Pakistan where at around $40 per household, the absolute costs of these sewers was much lower than in northeast Brazil. (School of Civil Engineering, University of Leeds, 2001).The precise trends will, of course, vary from country to country. The key point is that the per-capita cost of networked systems tends to reduce with increased housing and population density while that of on-site options remains roughly constant.

Taking Account of Sunk Costs

When estimating and comparing costs, remember that existing facilities represent 'sunk' costs; these have already been incurred and do not need to be reconsidered in cost calculations.

Consider an example in which every house has a septic tank, from which wastewater is discharged into an existing drain. It would be possible to fill in these septic tanks and replace the whole system with conventional sewers. Alternatively, the septic tanks could be connected to small-bore sewers to create a sewered interceptor tank system (SITS). When comparing the options, the cost of providing the septic tanks does not need to be considered, because they are already there. The cost of repairing any broken tanks, or periodically emptying the tanks must however be included in the financial comparison between conventional and SITS systems.

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