Global Review Finds Startlingly Little Evidence That Sanitation Systems Can Withstand Climate Change

When floods tear through a city, the damage is often measured in homes lost and lives disrupted. But one of the most dangerous and least visible failures happens underground and in backyards: latrines overflow, sewers rupture, and treatment plants drown, releasing human waste into the very floodwaters people are wading through. Sanitation is uniquely exposed to climate hazards, because it is physically woven into the water cycle, the soil, and the weather. Now, the first global systematic review of climate resilience in sanitation systems has delivered a sobering verdict: the evidence that any particular measure actually makes sanitation resilient is astonishingly thin.

The review, published in PLOS Water by a team led by J. L. Wallace of the University of Leeds, together with colleagues from the University of Oxford, the University of Bristol, the University of Technology Sydney, the World Health Organization, UNICEF, and other institutions, set out to answer a deceptively simple question: what is the evidence that specific technical, operational, and governance attributes or adaptation actions keep sanitation systems functioning during and after climate hazards? The answer, after screening nearly four thousand articles, was just seventeen studies that met the review’s inclusion criteria. From those seventeen studies, the team distilled twenty-seven distinct attributes or adaptation actions with potential to enhance resilience. None of them, the authors note, is currently considered in any existing global monitoring process.

The scale of the screening effort makes the small yield all the more striking. The researchers searched five major databases, including Web of Science, Medline, Scopus, CAB Abstracts and Global Health, in July 2024, following PRISMA guidelines for systematic reviews. Almost 4,000 returns were reduced to 3,461 unique articles for title screening, with two independent reviewers assessing titles, abstracts and full texts and a third resolving disagreements. Fifty-seven articles were selected for full-text review, and after exclusions, including eight that were inaccessible, only seventeen survived. Hand-searching reference lists added thirteen candidates, but grey literature searches and expert consultations produced nothing eligible. The dominant reason for exclusion was a lack of grounding in empirical or reported data: many papers proposed indicators of resilient sanitation without ever testing them against real-world cases.

The seventeen surviving studies split into two revealing clusters. Six came from the engineering literature, focused overwhelmingly on sewered systems in high-income countries, quantitative in style, and framed around the classic engineering resilience triad of robustness, redundancy and reparability. Eleven came from the international development literature, centred on non-sewered sanitation in lower-income settings, more qualitative in method, and notable for capturing something entirely absent from the engineering cluster: the experience of the user. Geographically, the picture is lopsided. One third of the studies were based in high-income countries, all addressing sewers or treatment facilities. Eight studies came from low-income countries, and five of those were conducted in Bangladesh alone, a country acutely exposed to flooding. The authors attribute this concentration partly to research bias toward simpler, more accessible interventions rather than complex, system-level solutions.

What the evidence does show is instructive. In low-income settings, the dominant strategy is what the review calls infrastructure stacking: households diversifying their sanitation options so that when floods or droughts knock out one option, another remains. During droughts, when water for flushing runs short, households fall back on multiple water sources for manual flushing or switch to non-flush and low-flush latrines. During storms that cut water supplies or flatten superstructures, resilience has come from stronger construction, temporary facilities, and stored water for flushing. Against flooding, the evidence centres on robustness of the latrine pit and its superstructure: higher cement content for structural integrity, trenches and earthen walls to redirect surface water, elevated bases and siting on higher ground, and informal quality assurance during construction. Crucially, almost all of these were autonomous household responses, not planned interventions by utilities or governments.

For sewered systems, the technical findings are more granular. Pipe material matters: sewers made of brittle vitrified clay fracture more readily under increased dynamic pressure than those of polyvinyl chloride or reinforced concrete, and concrete and clay pipes suffer higher blockage rates during droughts, partly because older pipes lack rubber gaskets that resist root intrusion and infiltration. Smaller-diameter sewers, being shallower and requiring less debris to clog, block more often, particularly in drought conditions. Iron manhole covers corrode on contact with saline stormwater. On the operational side, maintenance and timely pipe replacement reduce blockages, and one study demonstrated that drag-reducing polymers can raise sewer flow velocities by 60 to 70 percent by cutting friction losses. At treatment works, flood defences, expanded capacity, backup processes such as emergency chlorination, and early warning systems that trigger preparatory actions all appear in the evidence, while comparative studies under arid conditions found activated sludge treatment outperforming aerated lagoons for pollutant removal, with constructed wetlands similarly effective but less stable across seasons.

Yet the gaps dwarf the findings. Sixteen of the seventeen studies examined a single element of the sanitation service chain; only one took a genuinely system-wide perspective. Nine articles addressed latrines and containment, four addressed sewers, and three addressed treatment works. Not a single study captured resilience-building for the road-based conveyance of faecal sludge, wastewater, or supernatant, the trucks and informal workers that empty pits across much of the urban developing world. No studies provided evidence on pits and tanks as containment technologies, despite known vulnerabilities of septic tanks to flooding and backflow. Sea level rise, a slow-onset hazard that directly threatens the coastal locations where treatment works are typically built, was entirely unrepresented. Twenty of the twenty-seven identified attributes and actions address rapid-onset events such as storms, heavy rainfall and flooding, a bias the authors attribute to the simple fact that immediate disasters are easier to study within the time and resource constraints of research projects than gradual, less visible changes.

The review also raises an uncomfortable conceptual question: how much of what passes for climate resilience is simply good sanitation practice? Mapping the identified attributes against the Sanitation and Water for All definition of climate-resilient WASH services, which describes services that anticipate, respond to, cope with, recover from, adapt to, or transform based on climate-related events, the authors found that most evidence clusters around responding and coping, or falls into the category of good sanitation outright. Robust materials in flood-prone areas, for example, are good engineering practice regardless of climate change. Adaptation actions focused on system recovery and long-term transformation are notably absent from the evidence base, even though sector initiatives such as Systems Strengthening and Citywide Inclusive Sanitation are actively trying to reinforce the institutional fabric around infrastructure. The engineering notion of restoring a system to its functional state is itself contested, the authors note, because the pre-disaster state was one in which the system already failed.

Underlying all of this is a structural imbalance in who acts. In low- and middle-income settings, resilience is delegated to users, who bear responsibility for building and maintaining latrines without always having access to the knowledge, skills, and materials needed to do so durably, a situation that can produce maladaptation rather than resilience. Evidence on operational or enabling-environment strategies implemented by service providers or governments is minimal, and the review found a significant lack of studies connecting policy, institutional, regulatory, or financial actions by national or subnational governments with sanitation outcomes. Because government actions operate upstream, enabling users and providers downstream, their effects are indirect and hard to trace, which may explain why they vanish from the literature. The authors argue that effective resilience cannot be achieved through technical measures alone; it requires governance structures that create the conditions for adaptive strategies, cross-institutional collaboration, data sharing, and an end to the silos in which sanitation strategies operate in isolation from water, transport, and disaster planning.

The implications reach the highest levels of global policy. The review was conducted as part of a multi-year initiative by the WHO/UNICEF Joint Monitoring Programme and GLAAS to develop indicators for monitoring climate-resilient WASH within the Sustainable Development Goal framework, where no region is on track for universal sanitation access by 2030. The twenty-seven identified attributes offer a conceptual foundation and practical entry points for measurable indicators, but with only four of seventeen studies providing empirical measurements, the authors warn that indicators built from this evidence risk measuring successes while underrepresenting failure, trade-offs, and maladaptation. Their prescription is threefold: evaluate adaptation measures against observable service outcomes rather than assuming they work; shift from component-level studies to whole-system research that traces how disruption propagates across the sanitation chain, including the resilience of the workers who empty pits; and expand adaptation beyond infrastructure toward the governance, financing, and institutional conditions that determine whether systems merely survive climate hazards or genuinely transform. Until that evidence exists, the world is building sanitation for a changing climate largely on faith.

Subject of Research: Climate resilience of sanitation systems: a global systematic review of adaptation evidence

Article Title: Where is the evidence? A global systematic review of sanitation system resilience to climate hazards

Article References: Wallace, J. L., Wright, M. K., Camargo-Valero, M. A., Charles, K. J., Engebretson, B., Gordon, B., Gore, F., Howard, G., Johnston, R., Kohlitz, J., Mills, F., Moon, K., Nijhawan, A., Slaymaker, T., Takane, M., Willetts, J., & Evans, B. E. (2026). Where is the evidence? A global systematic review of sanitation system resilience to climate hazards. PLOS Water, 5(10), e0000474. https://doi.org/10.1371/journal.pwat.0000474

Image Credits: AI Generated

DOI: 10.1371/journal.pwat.0000474

Keywords: sanitation, climate resilience, systematic review, WASH, flooding, drought, faecal sludge management, sewers, pit latrines, SDG 6, JMP, adaptation