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To Sewer or Not to Sewer

Pasay City, Philippines. A boy in this stilted slum community collects plastic to re-sell.


For those of us who think the only decent toilet is one that flushes our wastes out of sight and out of mind, sewers seem essential – and in many countries, flushing with water is mandatory. But in the 19th century there were many advocates of ‘dry conservancy’ – composting toilets that recycled muck. In today’s water-conscious world, these have made a comeback. Ecological enthusiasts argue that providing thousands of litres of water treated to drinkable quality to every toilet user, only to have it soiled, discarded, and expensively retreated, is stupendously profligate with a precious natural resource. To provide that volume of water, under pressure, is not possible in many poor and water-stressed environments. Among donors, the pendulum has  therefore swung in favour of the ‘on-site’ solution, with sustainability the watchword of today’s sanitation assistance programmes. Some even refuse to fund sewer-based sanitation. But are sewers unfairly excoriated? We asked David Satterthwaite to make the case for sewers. And to give pits their due, we invited Mayling Simpson-Hébert to offer a brief riposte.


In praise of sewers
David Satterthwaite

Sewers and water-flushed toilets get a bad press nowadays. They are said to use too much water for a water-stressed world and the sewage they generate – if untreated – contaminates rivers and lakes. Nutrients that could be returned to the soil also go to waste. In cities with large populations living in squatter townships, sewers also seem too expensive and beyond local technical and financial capacities to construct and manage. This helps explains why most urban centres in Africa and Asia have no sewers at all, and where they do, they serve a small proportion of citizens.

However, the case against sewers has been overstated. Sewers are a quick, easy, efficient way of getting rid of the excreta and waste-water that all households generate. They are particularly effective for cities and in large and overcrowded neighbourhoods because they can shift large volumes, yet take up very little space. This is a major plus in tenements or squatter settlements where whole families often live in one small room. They also work well in multi-storey housing (most alternative systems do not).

Other advantages? They remove excreta completely from the home and neighbourhood. Pit toilets and septic tanks do not and, in most low-income neighbourhoods, they have to be emptied by hand – a difficult and dangerous job – because it is impossible to bring mechanized vacuum trucks into the alleyways. Flush toilets linked to sewers are generally easier to clean and keep down smells.

Health benefits? Sewers minimize the risk of human contact with excreta and reduce the presence of flies, which is an enormous health advantage. They protect groundwater from faecal contamination (most pit toilets don’t). They also take away households’ waste-water from cooking, laundry and bathing.

They generally serve as drains for rainfall and so prevent flooding – and they do this better than open drains that get clogged with rubbish. In schools, workplaces and public areas, they can stand constant use. This is a great advantage for heavily used community toilet blocks built and run by women in poor areas of Mumbai and Pune – a community-driven NGO-supported programme that serves over 500,000 Indian slum dwellers.

Sewers’ cost disadvantages are reduced at higher densities and where there are many multi-storey buildings; they can be cheaper per household than pit toilets if the cost of pit-emptying is taken into account. Water use can be kept down by pour-flushing (much less water per flush) and flushing with wastewater. There are communities – even in rural areas – that pipe away sewage to support crops or fisheries. Treatment systems can be decentralized and deploy local ecologies to prevent waterway pollution.

Some sewer initiatives have massively expanded sanitation in low-income city areas. The Orangi Pilot Project Research and Training Institute (OPP-RTI) today operates in most of Karachi’s informal settlements. With its technical support, local people in Orangi built and financed the installation of good-quality covered sewers. They collectively took responsibility for installing their toilets, building underground street sewers and local collectors. This brought the costs per house down to a fifth of what local utilities would have charged. This approach works particularly well where local governments provide the trunk sewers and treatment plants into which the neighbourhood sewer systems fit. OPP-RTI has supported similar initiatives elsewhere in Pakistan. These now serve hundreds of thousands of people.

Sewers are not always the best urban solution. They are inappropriate where water is very scarce – and where it isn’t feasible to extend them to lower-income settlements or those on city outskirts, so that fixating on sewers means that only the wealthy get served. Flush toilets also don’t work if water supplies are intermittent; and they pose serious health problems if there are no sewers or septic tanks to collect their wastes.

In the end, the key issue is not the technology but who makes the choice. This should be determined locally, not by what international agencies are prepared to fund. Choices should result from discussions with local residents, having duly informed them about realistic options. Externally designed solutions often do not work because they are inconvenient, too costly or inappropriate to local circumstances. The perfect design for an eco-toilet has limited value if children are frightened to use it because it is dark or they fear falling in the pit. Ecological sanitation will not return nutrients to the soil unless it is easy and cheap to get the compost to growers who want it.

Disputes over technology are not the only reason for lack of investment in urban sanitation. Governments often refuse to allow any improvements in ‘illegal’ squatter settlements, even if they house most of the city’s workforce. International agencies claim that urban populations are less poor than their rural counterparts. If this is so, why are urban child mortality and under-nutrition rates so high in many Asian and African countries?

Why, after 50 years of development assistance, are hundreds of millions of urban dwellers forced to defecate in the open or into plastic bags? If the reluctance to fund urban sanitation were turned around, donors would need to learn how to support local choices influenced by those who want and need the toilets and are prepared to contribute to the system they desire. If this happens, sewers will once again have a vitally important role in many urban locations.

David Satterthwaite is a senior fellow at the International Institute for Environment and Development in London.


In   praise   of pits
Mayling Simpson-Hébert

Sometimes the best solution is the easiest solution, and that is certainly true when it comes to serving most of the people on the planet without sanitation. The simple pit, with its bacteria, insects and worms, provides nature’s reply to the vexed question of how to provide them with toilets.

Before there were sewerage systems, nature recycled faeces deposited on the ground. Wriggly creatures broke it down or sunlight dried it out, or both. Animal excreta provide the nutrients that plants need to grow, then animals consume the plants as food, and so goes the cycle.

This is the theory behind ‘ecological toilets’: the replication of nature’s processes without requiring water for flushing or polluting rivers and lakes with sewage, and providing a nutrient-rich compost for growing food. They are most suited to rural areas, but some models are also used in towns.

The simplest eco-toilet is the Arborloo. A slab is placed over a metre-deep pit which, when full, is planted over with a fruit tree. Soil and ash are added after every use preventing smells and flies and improving the compost. Very popular in Ethiopia, tens of thousands have been constructed since 2006 and are seen there as the solution of choice in meeting the Millennium Development Goal on sanitation. 

The Fossa Alterna is a double-pit affair. Pits are alternated annually and the compost is removed and used as fertilizer after a year of decomposition. This design is popular in Mozambique.

The Sky-Loo sits above ground. Below it, a bucket receives faeces, to which soil and ash are added. Every two weeks the bucket is removed and the contents taken elsewhere for composting. Urine is diverted to another receptacle, and used directly as fertilizer on crops. These have been introduced successfully in Zimbabwe and Uganda.

Double-chamber eco-toilets have twin pits built above ground and used alternately, while urine is diverted away. Ash assists the drying process. While these toilets do not produce compost, the carboniferous powdery substance is good for conditioning agricultural soil. These designs are particularly popular in China and Mexico, where hundreds of thousands are in use.

Finally, pits can produce bio-gas to be used as cooking fuel, solving the problems of kitchen waste disposal, air pollution, and saving firewood collection.

Sewerage systems do not have any of these advantages, but worse, they consume and pollute large amounts of clean water, which, when discharged, can cause further pollution. All this grey- and blackwater output needs cleaning again for re-use. How inefficient is that? Sewerage systems have advantages for crowded urban areas, but for small towns and rural areas, the simple pit is best.

Mayling Simpson-Hébert is a regional water and sanitation advisor for Catholic Relief Services in Nairobi, Kenya, and co-author/editor of Ecological Sanitation, Stockholm Environment Institute, 2004.

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