Field testing reveals critical insights for adoption and commercialisation of non-sewered sanitation systems. Sonia Grego, lead author of a new book on the subject, explains.
Despite the United Nations Sustainable Development Goal 6.2, which calls for safe sanitation for all by 2030, an estimated 43% of the global population still discharge household wastewater without safe treatment. Unsafe sanitation – particularly in the Global South – drives preventable deaths, raises healthcare costs, depresses economic productivity, and contributes to water scarcity and vulnerability to climate change.
Sewered infrastructure is often seen as the gold standard for sanitation. Yet, sewers are not always feasible, especially in densely populated urban settings that rely on on-site systems such as septic tanks and ventilated pit latrines. While widespread, these solutions typically provide only partial treatment, are poorly maintained, and generate large volumes of faecal sludge that must be managed safely.
In response, initiatives – most notably the Gates Foundation’s Reinvent the Toilet programme – have catalysed an emerging area of engineering R&D and the development of new on-site solutions. These ‘non-sewered sanitation systems’ (NSSS) aim to meet stringent standards for pathogen and pollutant removal, enabling safe reuse or disposal of treated effluent and solids without relying on sewer networks.
Why is non-sewered sanitation different?
Unlike conventional on-site systems, NSSS technologies are sophisticated. They employ multi-stage processes that separate and treat waste and often integrate electro-mechanical components such as pumps, valves, and sensors, as well as electronic controls. This complexity makes them closer to compact treatment plants than to septic systems.
Over the past decade, significant R&D by universities and companies worldwide has advanced these technologies. A critical step toward technology maturity is field testing: validating system performance under real-world conditions. Field testing not only exposes technologies to diverse environments but also brings user behaviour, cultural context, and logistical realities into focus. For sanitation innovation to succeed, engineering development must incorporate the participation, feedback, and day-to-day experience of end users.
The realities of field testing
Field testing NSSS technologies is demanding. Systems must operate reliably outside the laboratory, in conditions that reflect both geographic and cultural realities. Success requires technical expertise, robust logistics, trust with local communities, sensitivity to user preferences, and continuous communication among stakeholders.
Recognising this, the Gates Foundation established dedicated third-party field-testing platforms in India, South Africa, and Thailand. Over eight years, these programmes evaluated more than 30 technologies, providing a structured environment to accelerate development and generate comparable data.
While many field campaigns have produced reports and peer-reviewed studies, much of the knowledge is fragmented and often focused on successes. Yet valuable insights come from challenges and failures. A recent book Engineering Field Testing of Non-Sewered Sanitation Systems: A Compendium of Lessons Learned (an open access publication, published by IWA Publishing) seeks to capture and distill these lessons to guide future practitioners. Below are some examples taken from the publication.
Lessons learned
Assumptions vs reality
Design assumptions about wastewater quantity and composition often prove inaccurate. Systems typically specify a capacity (e.g., up to 1000 l/day) and assume a certain ratio of urine to faeces. In practice, user behaviour varies widely and assumptions about wastewater quantity and composition were erroneous.
Some systems were found to fail due to overloading, while others malfunctioned when underloaded with solids. For example, at a school in Durban, South Africa, the expectation that toilets would be used mainly for urination was contradicted by actual use patterns, leading to unexpected performance issues.
Tracking toilet and water usage through meters and counters emerged as essential. Water consumption in washing culture was found to depend on the site and its users, and accurate measurement was critical to interpreting system performance.
The importance of baseline conditions
Unexpected influent characteristics created additional challenges. At one test site, extremely high water hardness caused mineral scaling on electrodes and fouled other critical treatment components – a water property irrelevant for pit latrines but critical for NSSS technologies. Baseline water chemistry measurement before deployment helps prepare and mitigate for this issue.
Analytical demands
Evaluating NSSS performance requires both conventional wastewater laboratory methods and new adaptations. Unusual properties of the samples required modification of standard protocols. Portable instruments capable of real-time measurement were indispensable for time-sensitive parameters (e.g., chlorine, turbidity). Pursuing ISO accreditation for a laboratory supporting NSSS field testing enabled results to be recognised across countries and regulatory systems.
Financing a field-testing campaign
A major consideration for undertaking field testing of a NSSS is estimating a realistic budget. We examined the major variables and drivers of cost, provided historical budget data, and shared tips on how to be more cost-efficient. In particular, there was economy of scale in testing multiple technologies at the same site and through the same programme, especially when core personnel were covered under a multi-year capacity grant that ensured retention of skills and knowledge.
Engaging with users in communities
Stakeholder engagement was an essential component spanning across all field-testing activities from site selection to decommissioning. Field testing required gaining permission for installation at test sites where users would have access to a new sanitation technology. Community engagement was especially important for site selection and preparation. Early and clear communication with the end users of the systems was paramount to establish trust and build relationships for the success of the test site. Frequent communication led by a dedicated liaison team was required at the inception of the testing, when any changes were made to the field-testing plans, and importantly at the conclusion of the project. In some cases, the test prototype offered participants a higher level of user experience than their original sanitation system, so the social impact of removing the test system had to be considered and expectations aligned.
Looking forward
As urban populations expand and climate pressures mount, compact and resilient non-sewered sanitation systems that meet stringent treatment thresholds become increasingly relevant. Technologies that operate at the household scale have yet to reach maturity and commercialisation. Moving forward, field testing will be needed along every step of the development process to achieve robust engineering and successful adoption.
The author
Sonia Grego is Associate Research Professor, Electrical and Computer Engineering Department and Associate Director, Center for WaSH-AID at Duke University, USA, and is lead author of Engineering Field Testing of Non-sewered Sanitation Systems: Compendium of Lessons
More information
Engineering Field Testing of Non-sewered Sanitation Systems: Compendium of Lessons
By Sonia Grego, Ruth Cottingham, Thammarat Koottatep, Atitaya Panuvatvanich, Susan Mercer, and Sarah Hennessy
Available as an Open-Access ebook
eISBN: 9781789064971
See: www.iwaponline.com
