Introduction

Inadequate sanitation is associated with numerous and varied health risks1. There are multiple sources of faecal environmental contamination from inadequate sanitation systems and multiple pathways for exposure2,3. The presence of a toilet is therefore an insufficient measure to indicate whether positive health outcomes are likely to be achieved by sanitation improvements4, hence numerous authors critiqued the Millennium Development Goal target, expressed solely in terms of access to toilets5,6,7,8. The Sustainable Development Goal (SDG) target 6.2 of safely managed sanitation services aims to address these limitations by considering the management of excreta from the toilet to final treatment and disposal9. The Joint Monitoring Programme (JMP) led the development of global indicators and standardised core questions to enable consistent and practical classification of sanitation services for national and global monitoring (see Table 3)10. However, these indicators do not cover all aspects of safety, such as those outlined in WHO guidelines on sanitation and health1. The guidelines suggest countries agreeing to the SDG framework should routinely monitor and report on the global indicators, as a minimum, and suggest these are complemented by more nuanced and contextual regional and national indicators. The JMP proposed some expanded indicators, but these focus on expanded definitions of toilet access, for example, privacy of toilet use, and include limited expanded indicators related to the safe management of containments, emptying, conveyance and disposal10. Safely managed sanitation as defined for global monitoring, while a significant improvement in monitoring access to improved toilets, should not be assumed to indicate a service level that protects against many key faecal transmission pathways. Since what doesn’t get measured doesn’t get managed11,12, relying on global indicators to prioritise investment may result in sanitation improvements that do not address critical health risks.

Despite debate and research on other aspects of SDG 6.2, there has been little assessment of the indicators for safely managed sanitation services nor exploration of the complementary indicators that could address the gaps. Numerous publications have critiqued and suggested improvements to the classification of shared toilets as limited sanitation13, the monitoring of progress of lower service levels14, the means of implementation targets15,16, and explored alternatives for monitoring safely managed water services17. However, there has been little discussion on the formation and scope of the indicators for safely managed sanitation services, and even uncertainty about how services will be measured as safely managed16. The opinion piece by Rose et al. defined safe sanitation through a communal social lens as based on the ‘social construct that lies at the intersection of knowledge, societal engagement, and controls’18. Rose’s paper highlighted the role of the community in monitoring but did not review the indicators for safely managed sanitation or propose alternative indicators relevant to their definition18. Beard et al. highlighted the challenges to assessing on-site systems and the need for revised categories for improved sanitation facilities, yet they did not review indicators related to safe management across the service chain19. One paper proposed complementary indicators for safely managed sanitation services for national monitoring in Austria20. This provided valuable insights for high-income contexts with predominately sewerage services, yet was less applicable for low- and middle-income countries with predominantly on-site sanitation.

National and subnational decision-makers should not rely on global monitoring alone to inform investment. Globally defined indicators for water and sanitation may not adequately capture the national realities and challenges faced by individual countries or best suit the needs of individual countries to assess progress towards national goals20,21. Beard et al. argued that for urban sanitation, global monitoring efforts do not provide a clear picture of the challenge of managing excreta at the city scale and that the current indicators have a limited ability to inform policy and action19. This paper does not intend to critique the objective and approach of the SDGs or indicators used for global monitoring but to highlight that these indicators are an initial approach to define a ‘safely managed sanitation service’. Indeed, the 2030 Agenda for Sustainable Development recommends that global indicators be complemented by indicators at the regional and national levels, which will be developed by Member States22. The Guidelines on Sanitation and Health also suggest more indicators are needed at the utility and sub-national levels to inform local programmes and actions1. Although the number of countries able to report against safely managed sanitation has increased, significant data gaps remain, particularly regarding on-site sanitation23, making it an opportune time to inform the scope and approach to monitoring sanitation.

Beyond those currently assessed by the global indicators, there are a range of additional exposure pathways associated with inadequate sanitation systems and their management. Animal access to uncovered or inadequately protected faeces can transmit excreta and pathogens to people, surfaces and food, especially in dense settings or places where animals and humans are in close proximity24,25,26. Inadequate subsoil treatment of leachate from unsealed on-site sanitation can contaminate groundwater supplies used for drinking water, with contamination risk influenced by toilet and containment type, soil type, groundwater level and proximity to wells27. Poor operation and management of sanitation can also increase exposure to faecal pathogens. Infrequent emptying of on-site sanitation is associated with an increased likelihood of overflowing, malfunction or reduced performance2. Infrequent emptying can also lead to unsafe emptying practices, such as entering the pit to remove hardened sludge or informal emptying practices such as wash out, putting both the workers and public at risk of exposure2,28. The health risks sanitation workers face during emptying have been increasingly recognised, including direct exposure to faecal pathogens and risks from working in confined spaces29,30.

While environmental sampling and detailed health exposure studies and models have improved our understanding of health risks, household surveys can assess potential exposure pathways at a larger scale and lower cost. Several tools, models and detailed research studies have developed methods to investigate critical faecal exposure pathways25,31,32,33. While they have been valuable in demonstrating the high concentration of pathogens in the environment and need to consider multiple exposure pathways, they typically require high skills or equipment and can be difficult to conduct at scale. Household questionnaires, while limited in simple questions and self-reporting, benefit from capturing sanitation data at scale for a relatively low cost when included in broader surveys. Assessment of indicators of pathogen exposure pathways cannot ensure that a system provides 100% protection against human contact with excreta; however, it can point to common failures in sanitation systems that increase the risk of exposure to prioritise improvements or further in-depth investigation. There remains an opportunity to expand household monitoring to better assess and prioritise potential exposure pathways at a larger scale than the field-based exposure assessments.

Recognising that global monitoring is necessarily limited for simplicity and comparability, this paper proposes complementary indicators that could be incorporated into household monitoring to provide a more comprehensive assessment of on-site sanitation focusing on faecal exposure pathways. While research on other aspects of SDG 6.2 led to debate and refinement of indicators (e.g., shared sanitation) for the assessment of safely managed services, as noted above, previous research identified the need for complementary indicators yet did not suggest potential indicators relevant to areas with predominately on-site sanitation, such as is common in low- and middle-income countries. SNV, an international non-government organisation, conducted baseline monitoring between 2018–2019 in 34 urban and rural districts across seven countries to inform and monitor progress of their sanitation programmes. Trained enumerators conducted surveys of 31,784 households, which included global core questions and supplementary questions related to additional exposure pathways as well as qualitative assessments of service provision. The data from health-related household questions were assessed to compare five complementary indicators with the equivalent global sub-indicators for improved, contained and emptied on-site sanitation. This research evaluated the extent to which consideration of critical exposure pathways reduced the proportion of systems classified as safely managed on-site sanitation and analysed the contexts or conditions in which different indicators may be more or less important. This research aims to address the gap in tested complementary indicators relevant to on-site sanitation that could be incorporated into sanitation monitoring systems. The research is timely as national WASH monitoring frameworks continue to be updated to improve reporting against the SDGs, and these relevant complementary indicators to enhance understanding of local health risks and inform sanitation investments.

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