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Stockholm Junior Water Prize winners bring faster flood warnings to small communities

When heavy rains hit, minutes matter. A few extra moments of warning can mean the difference between reaching safety before a flood or being caught by rising waters. That urgency drove German students Jana Spiller and Niklas Ruf to design WarnMe, a low-cost, open-source flood warning system for small towns and rural communities.

20/10/2025
Water News Floods Making Waves

Spiller and Ruf’s project, which won the Stockholm Junior Water Prize for 2025, grew out of personal experience. Their hometown in southern Germany, Ochsenhausen, experienced flooding in 2016 and 2024, damaging their school and local property. The problem is that while many cities have flood warning systems for large rivers, more remote communities don’t always have similar systems for smaller rivers and streams.

“As a global water technology leader, we know the sector needs new talent. This prize is about bringing in fresh perspectives and ideas. Seeing the courage and creativity of next-gen innovators motivates young people everywhere and our own people at Xylem. It drives purpose. And it challenges us to think differently – often more simply and affordably.”
Claudia Toussaint, EVP, Chief People & Sustainability Officer at Xylem

Below is an interview with Spiller and Ruf, where they describe how WarnMe can help communities of any size better prepare for floods.

Why don’t more small towns have flood warning systems?

Spiller: All over the world, rainfall events are becoming more intense, causing rivers and streams to rise rapidly. Large rivers, like the Rhine River in Germany, are already well monitored, so we can quickly see changes in water levels. But small rivers and streams often go unmonitored, even though their flooding can be just as dangerous.

Ruf: Flood monitoring stations on a large river can cost tens of thousands of dollars. That amount of investment isn’t always possible for smaller waterways, which leaves rural areas more vulnerable to flooding.

How does WarnMe help small towns implement a flood warning system?

Spiller: Our system focuses on small streams that have been historically overlooked. These waterways can rise quickly during storms, so WarnMe provides early flood warnings by combining local sensors, real-time evaluation, and integration with flood hazard maps.

Ruf: We mount infrared and ultrasonic sensors under bridges, which measure the distance to the water surface. The infrared sensor costs about $50, and the ultrasonic sensor about $85. The sensors send data to a server, where it is evaluated by an algorithm. If a flood is detected, the system automatically sends a warning to users through our mobile app.

How did you learn about this innovative technology as students?

Ruf: In Germany, we have student research centers where we started studying robotics in the fifth grade. As we got older, we switched to studying LoRaWAN technology – the wireless network we now use to transmit our sensor data. We first learned about the technology at a workshop on it and then taught ourselves how to build it into our WarnMe system.

What is LoRaWAN technology and why did you choose it?

Ruf: We live in a rural area with limited mobile coverage, so LoRaWAN – which stands for long-range wide area network – is perfect. It lets us transmit data without relying on mobile service, and it is extremely energy efficient. Our system can run for an entire year on just two AA batteries.

Spiller: Another advantage of our WarnMe system is that you can install it on existing infrastructure, under bridges, which also lowers the cost.

How do you hope people or communities will use WarnMe?

Spiller: We designed WarnMe as an open-source project so that anyone, individuals or local governments, can access and use it. Right now, we’re looking for partners to help us further develop the system and for communities who want to install the monitoring stations so more people can receive early flood warnings.

Ruf: Winning the Stockholm Junior Water Prize had an awesome networking effect. Just three minutes ago, I received a text message from someone in Kazakhstan interested in the system. That amount of global interest shows how much potential the system has.

Why are you hopeful that technology can help solve global water challenges?

Spiller: Meeting the other finalists in Stockholm was inspiring. Everyone was so passionate and knowledgeable – it showed how innovation and collaboration can make a real difference in tackling water challenges.

Ruf: Technology is advancing so quickly and becoming more accessible every day. Tools that used to cost thousands of dollars are now readily available – I now even have an AI assistant helping me with my programming! The radar sensor that measures the speed of water in our system was out of reach just a few years ago. Technology keeps getting better, and that gives us hope.

Investing in a water-resilient future

Innovations like WarnMe show how accessible technology can strengthen water resilience in communities of any size. As digital tools become more affordable and adaptable, more local leaders will be able to protect lives and infrastructure from unpredictable weather events – building a safer, more sustainable water future for everyone.