Beyond the Flush: Measuring Sustainable Sanitation for a Changing World

As we mark World Toilet Day, this year’s theme, “Sanitation in a Changing World,” prompts us to consider more than just the provision of toilets. It urges us to ask a more pressing question: “How can we ensure that our sanitation systems remain genuinely sustainable for the future?” With less than five years left until 2030 and two billion people still lacking access to safe sanitation, the challenge is daunting and requires urgent attention from all stakeholders. According to dos Santos et al. (2025), achieving environmental sustainability goals at the current rate could take up to 500 years. In a world grappling with new ecological and economic pressures, selecting an appropriate sanitation solution for each community is crucial.

Introducing the Sanitation Sustainability Index (SSI) as a Potential Solution

In a recent study, Hashemi (2020) offered a tool for navigating this complexity: the Sanitation Sustainability Index (SSI). This index is designed to evaluate and compare different sanitation options for a community before implementation, thereby saving valuable time, money, and resources. As presented in Figure 1, the SSI provides a comprehensive score by examining three key areas.

• Technical Aspects: How efficient is the system in terms of water and energy usage? How effectively does it recycle the waste?

• Economic Aspects: What are the capital and maintenance costs relative to local norms, and can the system generate economic benefits?

• Social Aspects: Is the system culturally acceptable to the community, and does it enhance public health?

Figure 1. Structure of the Sanitation Sustainability Index and Evaluation Criteria (Hashemi 2020)

Putting the Index to the Test in South Korea

To illustrate the practical utility of the index, Hashemi (2020) applied it to evaluate two different sanitation systems for a community in Seoul, South Korea: a traditional septic tank and a modern resource-oriented sanitation (ROS) system. An ROS system is designed to treat and recycle human waste, often converting it into a fertilizer. The results were significant. As depicted in Figure 2, the ROS system achieved a significantly higher sustainability score (SSI = 0.71) than the septic tank (SSI = 0.42). Although the community was more accustomed to the septic tank, the ROS system outperformed it in both technical and economic dimensions. Its ability to efficiently recycle waste and produce valuable resources offers distinct advantages.

Figure 2. Comparison of SSI for septic tank and ROS systems in South Korea

A Flexible Tool for a Diverse World

What makes SSI particularly useful in our “changing world” is its adaptability. Rather than being a rigid, one-size-fits-all metric, the index was specifically designed to be customized to the local context. All variables, from water consumption to the average maintenance costs for existing systems, are grounded in the current norms of the specific community being studied.

This approach enables decision-makers to make informed choices that are socially acceptable, economically viable, and environmentally sound for unique circumstances. By focusing on factors such as waste recycling and potential economic benefits, SSI helps communities build resilient sanitation infrastructure that not only disposes of waste but also generates value.

On this World Toilet Day, as we strive to achieve clean water and sanitation for all by 2030, as per the UN’s Sustainable Development Goal 6, tools like the SSI illuminate the path forward. They remind us that the most sustainable solutions are not just about constructing more toilets but about building the right toilets, intelligently and sustainably, for the communities that need them most.

References:

• dos Santos, L. C. T., Giannetti, B. F., Agostinho, F., & Almeida, C. M. (2025). Modeling a comprehensive multi-criteria, multi-period framework for assessing global sustainability performance: Insights from 164 selected countries. Ecological Modelling, 507, 111167.

• Hashemi, S. (2020). Sanitation Sustainability Index: A Pilot Approach to Develop a Community-Based Indicator for Evaluating the Sustainability of Sanitation Systems. Sustainability, 12(17), 6937. https://doi.org/10.3390/su12176937.