Wednesday, 16 January 2008

Simplified/condominial sewerage − 1

Simplified/condominial sewerage was first installed in Rocas, a low-income area in the city of Natal in northeast Brazil, in 1982. The installation cost per household was USD 325. CAERN (the local state water and sewerage company) borrowed the money for the whole scheme from the then National Housing Bank and calculated that it could pay back this loan over the 30-year term by surcharging the monthly water bill by only 40% (rather than the usual 100% for households, obviously not poor households, served by conventional sewerage). At that time each household in Rocas had a yard-tap level of water supply service, which was not metered, for which it paid the so-called minimum tariff which was then USD 3.75 per month. So the simplified sewerage charge was (0.4 × 3.75) − i.e., only USD 1.50 per month, which was clearly affordable. Similar installation costs were found in Brasília and the Federal District (1998 costs: USD 170−340, vs. around USD 500−1500 for conventional sewerage). In the mining town of Parauapebas in the state of Pará in north Brazil the cost in 1997 was only USD 56, vs. USD 94 for conventional sewerage. Three other important points are (i) in Natal simplified sewerage was found to be cheaper than on-site sanitation (pour-flush toilets and leach pits) when the population density was above 160 persons per hectare (which is not especially high); (ii) the local water and sewerage agency can accept the system simply because it is sewerage (generally it won’t have anything to do with on-site systems, regarding these to be the responsibility of the municipal environmental health office); and (iii) the periurban residents commonly like it because it is very similar to what the rich have (actually in Brasília rich areas are also served with simplified sewerage). The report The Experience of Condominial Water and Sewerage Systems in Brazil written by José Carlos Melo (who developed the basic concept and has designed many systems including the first one in Rocas) is well worth reading. So, in high-density periurban areas simplified sewerage is almost always the cheapest and the best (certainly, a very good) form of sanitation. Why would you want to choose anything else? [Well, you might if you were an ‘EcoSanologist’, but more on periurban EcoSan later …]