ALICANTE, Spain — Sitting underneath cities, sewers typically conjure the image of dark tunnels swirling with dirty water and accompanied by a stench that has most people holding their noses. While they may not be the most glamorous of development interventions, sewage systems — networks of pipelines that transport waste and stormwater from sinks and toilets to treatment plants or receiving waters — contribute to a population’s health, boost gender equity, and reduce poverty.
Despite the benefits, experts say they might not always be the right fit.
A toilet connected to a functioning sewage system means waste is disposed of in a way that does not contaminate drinking water, helping to combat multiple waterborne diseases. It also provides women and girls with a place to defecate safely, prevents inland flooding, and eliminates time — which could be spent working or learning — looking for a safe space to go to the toilet.
According to the Centers for Disease Control and Prevention, a sewage system is vital to improving health but is often not implemented due to a lack of resources, infrastructure, available technology, and space. Only 68% of the global population has access to basic sanitation, and only 39% of people have access to safely managed sanitation.
“The next big thing is the ‘last mile’ connection to sewers,” said Eden Mati Mwangi, acting country program manager for Kenya at Water & Sanitation for the Urban Poor.
Only three main cities in Ghana have a sewage system, and sewers in Kenya are estimated to reach just 19% of the population. Instead, many turn to latrines or septic tanks, Mwangi said, but these require the emptying of waste into the environment, which then contaminates it.
While sewers might be the ideal long-term solution, experts say their implementation as a costly and large infrastructure project may not always be the best option.
Global criteria aimed at quantifying the problem of poor sanitation is underestimating the problem in urban areas, according to a report by the World Resources Institute.
“It’s key that we don’t think there’s one gold standard and that’s sewers, and expensive sewers, and that’s the best and everything else is somehow a lower-quality service,” said Lindsay Stradley, co-founder of Sanergy, a sanitation-focused social enterprise. “We need to understand factors such as density, water availability, topography, cultural preferences, and finances from an initial investment, as well as the means to operate and maintain any option going forward.”
“What we’re interested in is thinking about when sewers are the best and most appropriate solution,” said Barbara Evans, chair in public health engineering at the University of Leeds, on a panel at this year’s World Water Week event. In any given city, sewers on their own would not be the only solution to improved citywide sanitation, she added.
When are sewers the best option?
“Sewage systems are brilliant if the conditions are right and the capacity is there. ... But wherever you look, conventional sewage systems are expensive,” said Frank Greaves, WASH adviser at Tearfund.
Evans said at World Water Week that, particularly in highly dense areas, sewers are often the cheapest option. “And they very often have lower operational reliabilities than a lot of alternatives,” she said.
“It’s key that we don’t think there’s one gold standard and that’s sewers.”— Lindsay Stradley, co-founder, Sanergy
WSUP puts the cost of a conventional sewage system at $1,500 per household.
“For many NGOs like ourselves working with really poor communities, perhaps our goal is really about basic sanitation, so we would be staying with on-site sanitation [such as pit latrines, composting toilets, and septic tanks], particularly for our poorer rural communities and humanitarian situations for a while to come,” Greaves said.
In Kenya’s informal settlement of Mukuru, WSUP and Nairobi City Water and Sewerage Company are piloting an approach that could make sewage systems more affordable. A conventional sewer must be laid straight and deep, Mwangi said, but this project involves a simplified sewer, which uses plastic pipes that can bend, be laid at a shallower depth, and cost less at between $150 and $325 per household. “Simplified sewers are the future. We just have to get it right, learn what is working and what isn’t working, and improve on that,” she said.
For Stradley, the installation of the infrastructure is another big challenge. “Where you have dense populations without sewage infrastructure, putting in new sewers — even low-cost ones — [there is] still a large challenge of moving people temporarily. That’s very expensive and political,” she said.
Even if sewage mains are close by and a simple connection is seemingly all that is needed, there is still the challenge of operations and maintenance, Stradley said. This includes the cost of continued maintenance and the building of local capacity to ensure pipes can be fixed if broken. And all of this will not be worthwhile unless communities take up the service.
Ruth Kennedy-Walker, a water supply and sanitation specialist at the World Bank, said on a panel at World Water Week that a World Bank study had indicated that 17% of Peruvian households are not connected to the sewer network but had a sewer main in front of their homes. This increased to 34% in the city of Lima.
In a guide presented at World Water Week but yet to be formally launched by the World Bank, reasons for nonconnectivity include high upfront costs, competing priorities, a lack of stable income, high transaction costs, and a lack of information on the benefits and process around paying for the connection.
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“The construction and expansion of sewers comes at a high financial cost, which is meant to be balanced by the public health, environmental, and associated benefits of safely connecting and managing wastewater,” said Kennedy-Walker. “Consequently, when households do not connect the network, return on investment is not achieved and associated benefits are not met.”
Kennedy-Walker said it is important to work with communities to make sure they understand the benefits of being connected. With the World Bank-financed Zhejiang Rural Water Supply and Sanitation Project in China, work on laying sewer pipes to connect all the households in the village of Dongchen only began once 75% of the villagers agreed to it.
Another factor when considering sewage implementation is water access. Sewers need water to operate, and they may not be viable in water-stressed contexts, Greaves said. For example, while some larger cities have sewers, he said that many places in India have chosen to stay with on-site sanitation options because of a water shortage. The country is seeing 65% of its reservoirs run dry, and 21 major cities could run out of groundwater this year.
Rather than taking a blanket approach to sewage implementation, Stradley said she believes the sector should be looking at ways of combining sewers with other sanitation solutions. “Deciding what sanitation service delivery model — sewered, nonsewered, what type of nonsewered, and even now what type of sewered … any one area is going to need a distinct combination of those things.”