We started working on the article over three years ago by looking at existing water footprint concepts. We quickly realised that we wanted something simpler, more consistent and more comprehensible. At the same time, we wanted to integrate the preliminary work of our colleagues. With this in mind, began a very long phase of elaborating different approaches. Mostly these became more and more complicated, I still remember a very challenging case differentiation of green water use with respect to land cover changes, until we had to stop, drastically simplify the approach and start from scratch. In short, it was a tenacious period of tinkering in which we did not always see the goal clearly in front of us. A multitude of different concept drafts is witness to this lengthy process. Finally, a major breakthrough was breaking down the water footprint to a very simplified hydrological input-output analysis. The key to the solution was a combination of our different expertise: Martina Flörke explained the hydrological basics, which I translated into a life cycle assessment, while Stefan Bringezu always took a systemic view of our work. After that, the knot was broken, so to speak, and we were able to create our main figures, which can be found in the article and describe our concept of the water footprint. Now that it has been proven in application to a case study, we will take our concept further to demonstrate its strengths. What we would like to see in the future: That our and similar concepts are used in practice to identify hotspots of environmental impacts in general, and water use in particular, and to compare products and technologies in terms of their environmental impact at an early stage. We believe that decision makers can avoid problem shifting and prevent past mistakes only with this knowledge.