To develop students' capacity for science and to engage them productively in science and engineering practices, science education reform efforts have focused on supporting teachers' development of conceptual understandings through engagement with both disciplinary content and practices, including science teaching at the primary level. One topic of importance for primary science instruction focuses on Earth systems and, in particular, hydrological phenomena. Scientific modelling provides an effective, practice-based strategy for students' conceptual development of water. This manuscript focuses on longitudinal research with four primary inservice teachers' learning and engagement in model-based teaching about water over three years, investigating teachers conceptualizations and practice modelling water related phenomena over time. Findings from the study indicate while each teacher had individual trajectories in conceptualising and enacting scientific modelling in the classroom, we observed unique approaches within teachers. All teachers had a unified understanding and enactment of modelling in their first year. Over time, however, their focuses on modelling diversified and there were clear patterns of preference on some modelling facets over others. Finally, while teachers' conceptualizations about modelling became more robust, implementation of modelling only occurred in their practice as teachers were able to identify students' modelling needs.