Development and validation of a multi-tier diagnostic test on the water footprint concept

Purpose Conceptual understanding is essential for effective sustainability education, yet students often hold alternative conceptions about key environmental issues. The water footprint (WF), a multifaceted indicator of water use, is increasingly included in sustainability curricula but remains conceptually challenging. This study aims to describe the development and validation of the Water Footprint Diagnostic Instrument (WFDI), a multi-tier diagnostic test designed to assess undergraduate primary education students’ scientific and alternative conceptions of the WF. Design/methodology/approach The construction of the instrument followed Treagust’s principles for developing multi-tier tests and involved three phases: defining propositional knowledge statements, identifying students’ alternative conceptions through two qualitative pilot studies (n = 64; n = 94) and developing the final multi-tier tool. The WFDI was piloted with 56 students, after which minor wording revisions were made before its final administration to 238 students from three Greek universities. Findings The reliability of the WFDI was acceptable (Cronbach’s a = 0.866), and item analysis showed an appropriate spread of difficulty and discrimination values. The results indicate that the tool successfully exposes a sharp misalignment between student accuracy and confidence, revealing that pre-service teachers’ knowledge is often context-dependent and fragmented rather than structurally unified. Practical implications The WFDI provides Higher Education Institutions (HEIs) with a data-driven pathway to reform teacher-training curricula and to target specific sustainability competencies. Specifically, it is valuable for identifying undergraduate students’ initial ideas, developing and evaluating targeted instructional interventions, informing curriculum design and supporting future research on WF-related sustainability topics. Originality/value This study addresses a significant gap in sustainability education by developing the first validated multi-tier diagnostic instrument designed to assess a core and complex sustainability concept, that of Water Footprint. By explicitly linking psychometric data to conceptual change learning theories, the instrument moves beyond purely descriptive testing to reveal structural flaws in future educators’ systemic thinking about complex, global water-use systems.