Traditional water monitoring relies on physical and chemical testing, but this project broke new ground by using stable isotopes—natural variations in water molecules that act as unique identifiers. This is the first time that high-resolution isotope tracing techniques were applied systematically across such a wide range of urban environments globally. These novel methods enabled researchers to:?

• Trace water origins (surface water, groundwater, or reservoirs)?

• Detect evaporation losses in storage systems?

• Identify mixing between different water sources?

• Pinpoint contamination pathways faster than conventional methods?

The project’s findings are already making a difference in how cities manage their water. By identifying how water moves and changes within urban systems, cities can now plan and allocate resources more efficiently and respond more quickly to risks like drought, pollution, or overuse.?

“Understanding the seasonal shifts in our water sources has helped us better plan for dry periods and ensure consistent supply to our residents,” said German Esquivel-Hernandez, from the Water Resources Management Laboratory, Universidad Nacional, Heredia, Costa Rica.?

In Nepal, the findings have become part of everyday planning. “This project gave us the tools to trace where our water comes from and how it changes. That knowledge is now part of our daily decision-making,” said?Bijay Man Shakya of the Center of Research for Environment, Energy and Water, Kathmandu.?

Similarly, in Slovenia, the project supported real-time improvements to urban water quality. “The isotope data helped us identify blending zones in our network and optimize treatment processes,” said?Klara Zagar, Jozef Stefan Institute, Ljubljana.?

The strength of the project lay in its international collaboration. Researchers from 10 countries (Argentina, Costa Rica, Ecuador, Ethiopia, India, Morocco, Nepal, Romania, Slovenia and the United States of America) shared expertise and adapted isotope techniques to suit their local water management challenges. This exchange ensured that solutions were both scientifically sound and locally relevant.?

The research project’s legacy includes scientific advancements in isotope hydrology, the development of practical tools for water managers, training programmes that build global capacity and establishment of policy frameworks for sustainable water management.?

It also led to the publication of numerous articles in peer-reviewed articles and the training of researchers and utility professionals in the use of isotope techniques to manage urban water systems.?

Ricardo Sanchez-Murillo, a senior researcher at the University of Texas at Arlington who participated in the project, said:??

"The development and application of novel isotope tracer techniques during this coordinated research project have provided us with invaluable tools for understanding and managing urban water supply systems. These techniques will play a crucial role in ensuring the sustainability of urban water supplies in the face of growing water demand and climate variability."?

Today, cities are taking informed, data-driven actions thanks to this initiative—strengthening their ability to manage water more sustainably and adapt to the increasing challenges of climate change. By unlocking the stories told by water molecules, they are making smarter decisions and building more resilient and secure water systems for the future.?

A Scientific Forum on Atoms for Water will take place from 16-17 September 2025 at the IAEA Headquarters in Vienna, during the 69th General Conference. More information on the Forum is available?here.