Urbanisation in a changing climate provides specific challenges, but also opportunities, to reach SDG6 and the human right to water and sanitation (HRWS). Key challenges are inequalities and conflicts of interest in water resource distribution, overexploitation, pollution, and droughts and floods. The opportunities are improved stormwater harvesting, and circular approaches, using synergies between different water users. To sustainably manage urban water, it is necessary to know its flows and stocks and to make this information easily accessible to key stakeholder.

The Water Flow Diagram (WFD) includes a methodology to do integrated water balancing, to identify challenges and opportunities related and to visualize the result in one representation. It connects information related to Water Sanitation and Hygiene (WASH), Integrated Water Resources Management (IWRM), the Human Right to Water and Sanitation (HRWS).and assists in the creation of a joint vision to prioritise action. The aim is to empower municipalities and their stakeholders to work towards more integration and to reduce inequity and increase resilience and contribute to all indicators of SDG6.

The idea for a Water Flow Diagram emerged during an Aguasan meeting in 2020. Together with the Swiss Development cooperation (SDC), UNICEF, the Stockholm Environment Institute (SEI), the aid organization of the Swiss Protestant Churches (HEKS) and the Swiss Water Partnership (SWP) the concept was further developed. Three case study diagrams were elaborated and presented at the World Water Week in Stockholm 2021.

On the basis of positive feedback received, Eawag further developed the methodology and a user-friendly guide on how to generate a WFD. The methodology was presented at the World Water Forum in Dakar 2022 and the UN water conference in New York in 2023. This led to a joint commitment to the UN Water Action Agenda.

Currently, a methodology package is available here. Furthermore, controlled applications are going on in Brasil, Philippines, Senegal and Uganda. Additionally, the core team from Eawag, the Eastern Switzerland University of Applied Sciences (OST), and the Association of Swiss Wastewater and Water Protection Experts (VSA) are continuously improving and extending the methodology.

The most recent advancement resulted from the application to the city of Zürich: (1) different land uses were included to better quantify flows related to precipitation to understand the potential of nature-based solution for water management; and (2) a methodology to trace pollutants including nutrients and micropollutant from multiple sources and their fate in the environment.