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         Simplified Sewerage:
       Financial Cost Advantages



This graph has an important message: simplified/condominial sewerage can be cheaper than on-site sanitation systems.  At low population densities it is more expensive, but as the population density increases there comes a point at and above which simplified sewerage is cheaper. The graph is for the low-income periurban areas in the city of Natal in northeast Brazil where simplified sewerage was first installed in the early 1980s.  In this particular case simplified sewerage became cheaper than on-site systems at the relativley low population density of ~160 persons per ha.  See here for a Google Earth view of Rocas and Santos Reis (the part of Natal where simplified sewerage was first installed).

Graph of sewerage and on-site sanitation costs vs. population density

In periurban areas of Natal served with simplified sewerage the capital cost per connection (household) in 1983 was US$ 325 [it is much lower now*].  The water & sewerage company borrowed the money for the project from the then National Housing Bank and it calculated that it could repay this loan over 30 years by surcharging the water bill by 40% (rather than by 100% which was the surcharge for non-poor households served with conventional sewerage).  The periurban households had an unmetered yard-tap water supply for which they paid US$ 3.75 per month, so the charge for simplified sewerage was 40% of this - i.e., US$ 1.50 per month. There was no connection fee.  So it was a very low-cost pro-poor solution.
      For January 2008 charges see here.

Even if on-site sanitation systems are cheaper in capital cost terms, low-income households may be better off financially being served by simplified sewerage as the monthly payment may well be less than that to repay a short-term microcredit loan.  Moreover operation and maintenance is much easier with simplified sewerage as almost all the O&M is done by the sewerage service provider.

A final point: if a city or town has a sewerage system serving at least part of its area, then there will be at least some local knowledge (however imperfect) of sewerage and sewer O&M.  In contrast the city or town Department of Environmental Health may have very little experience of
on-site sanitation systems and the O&M required for, for example, latrine pit emptying.


      *See The Experience of Condominial Water and Sewerage Systems in Brazil (WSP, 2005)
.