Professor David Werner, Dr Alemseged Tamiru Haile, and and Dr Kishor Acharya


Everyone poops and pees. In sickness and in health. Which means that safely managing human waste is one of the world’s greatest challenges. On 19 November, UN Water observes World Toilet Day to celebrate what toilets do for us – from taking away our waste to protecting our health, safety, and dignity – and to draw attention to the plight of 3.6 billion people who lack access to a toilet. 

Children outside a pit latrine in Zambia

Toilets come in many shapes and sizes. About a quarter of the global population uses pit latrines. They typically consist of a concrete slab with a drop hole above a pit in the ground, covered by a basic shelter. Pit latrines provide a low-cost method for separating human waste from people. They provide basic sanitation for informal housing in many densely populated settlements of rapidly growing cities in the Global South. If well maintained, pit latrines decrease the public health risk of pathogen transfer between faeces, food, and people via vectors like water, fingers, and flies. However, there are concerns about groundwater pollution from pit latrines. 

Our fieldwork in informal settlements in Dar es Salaam with colleagues at Ardhi University in Tanzania showed that pit latrine sludge contains a thousand times more hazardous bacteria than shallow well water, and a hundred thousand times more hazardous bacteria than deep borehole water. These insights were obtained with the help of an affordable suitcase laboratory which we have developed to bring state-of-the-art molecular microbiology methods within reach of researchers in low and middle-income countries (Acharya et al., 2020).

Practical training in wastewater analysis at the Addis Ababa Water and Sewerage Authority

Our findings from Tanzania and Nepal (Acharya et al., 2019) confirm risks from pits to shallow wells and, to a lesser extent, deep groundwater resources. But even more, these findings highlight the risks to sanitation workers who empty the pits when full and provide sludge transportation and disposal services. In Ethiopia, we work with the Addis Ababa Water and Sewage Authority (AAWSA) and Addis Ababa University on improving occupational health and safety awareness among wastewater collection and treatment workers with the help of flyers, staff trainings and surveys. 

Our surveys of sanitation workers identified an urgent need to provide them with more personal protective equipment and showering facilities at their workplace. They also need hand washing facilities with soap for their waste collection trucks, so that they can sanitize hands easily before lunch breaks. During the COVID-19 pandemic, sanitation workers in Addis Ababa and beyond continued their essential services to households during periods of lock-down. These Covid heroes prevented the spread of infectious disease by maintaining sanitation while the city’s residents sheltered at home. They deserve as much recognition as the doctors and nurses in hospitals!

Sampling aquaculture pond water to monitor environmental spread of antimicrobial resistance in Thailand

Flush toilets provide an alternative sanitation solution to carry human waste away from homes. But without appropriate sewerage and end-of-pipe treatment, flush toilets may just translocate infection risks from more affluent cities to their poorer peri-urban neighbourhoods. Our work in Nepal demonstrated how inadequate wastewater management in the capital Kathmandu turns the Bagmati river into an open sewer, which poses a public health risk (Pantha et al., 2021). In Malaysia, we found increased numbers of multidrug-resistant bacteria in a river near sewage treatment plant outfalls (Ho et al., 2021). In Thailand, we elucidated the threats posed by inadequate urban wastewater treatment to peri-urban food production systems like coastal aquacultures (Thongsamer et al., 2021). In emerging economies, many of the city dwellers could afford to pay fees towards the costs of wastewater treatment, just like they pay daily for other infrastructure services. In Bangkok, Thailand, for example, the toll collected for each highway access or bridge crossing ranges from 25 to 100 Baht, while sensible proposals to collect 48 Baht per month from households for their wastewater treatment have been dragged down by politics since 2004 (Mrozik et al., 2019). Politicians in Bangkok and beyond should take note of surveys showing that most residents agree with plans to collect fees for wastewater treatment.

Mobile laboratory for molecular water microbiology at Birtley sewage treatment plant in the UK

Finally, those of us living in high-income countries shouldn’t feel too snug and consider what we are flushing down our toilets. Recently, when international travel was restricted during the COVID-19 pandemic, we applied the faecal pollution source tracking methods perfected with our work in Africa and South Asia to the UK. We were astonished to find that during storm events, the microbiome of an urban river in the UK closely resembles untreated sewage. In countries with an aging wastewater infrastructure like the UK, combined sewer overflows regularly discharge faecal bacteria and sewage litter into rivers. Poorly biodegradable baby wipes and sanitary pads, carelessly flushed down our toilets and drains, leave a long-lasting legacy in the environment that will be difficult to remedy.

Major investment into improving sanitation is thus required across the globe, in low, middle, and high-income countries alike. In Ethiopia, we are encouraged by AAWSA investment into modern laboratory facilities to monitor their sewage treatment plants which we support with staff training in good laboratory practice and quantitative microbial risk assessment. In India, we are encouraged by institutional investment into decentralized water infrastructures that reclaim wastewater to meet ground maintenance water demand (Zang et al., 2021). In the UK, we scrutinize the performance of toilets that use rainwater, or a mixture of water with pressurized air, to minimize the amount of potable water we waste when flushing toilets (Zang et al., 2022).

For those of us who have access to toilets, let’s celebrate what they do for us. Let’s be willing to pay for the safe treatment of our waste, and let’s celebrate, reward, and protect those workers, which provide us with essential sanitation services.

Funding for the research was provided by UK Research and Innovation (UKRI) via the Engineering and Physical Sciences Research Council (EPSRC), Biotechnology and Biological Sciences Research Council (BBSRC), and Global Challenges Research Fund (GCRF). Additional funding was provided by the Royal SocietyNewton FundBritish Council, Thailand Research Fund (TRF), and Department of Science and Technology (DST), India.

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