Water footprint which is not the water footprint: Critical review of the article by Müller et al. (2024).

This paper presents a critical analysis of the article "Comparison of cooling tower blowdown and enhanced make up water treatment to minimize cooling water footprint" by Müller et al. (2024), which claims to reduce the water footprint (WF) of cooling circuits. The WF concept, introduced in 2002, has evolved with two main approaches: the "volumetric" approach, quantifying water consumption, and the "impact-oriented" approach, assessing impacts associated with water usage. Müller et al.'s method is examined against these established methodologies. The analysis reveals that Müller et al. do not specify their WF approach, but their calculation suggests a "volumetric" WF focus. They claim WF reduction by minimizing cooling tower make-up water and blowdown discharge. However, this does not necessarily reduce the blue WF, as blowdown is typically a return flow that is not included in WF calculations unless it is discharged to another watershed or during a different period. Additionally, the grey WF impact is unclear due to insufficient data on pollutant concentrations in discharged water. The article also does not mention any characterization models or impact categories, making it unlikely that an "impact-oriented" WF approach was used. In conclusion, Müller et al.'s study does not align with established "volumetric" or "impact-oriented" WF methodologies. Instead of reducing water consumption (WF), it focuses on reducing water withdrawals. The use of the term "water footprint" appears to be a misapplication, taking advantage of its popularity. This misuse may mislead readers and underscores the need for rigorous review and critical assessment of published papers.