Prospective preschool teachers (PPTs) need to have learning experiences with the practice of scientific modelling to be able to design appropriate lessons as teachers. In the literature on research in science education, scarce experiences of PPTs in scientific modelling can be found. This study aims to fill the knowledge gap about PPTs' representations of water and its states by means of models. To this end, an analysis is made of the models designed by PPTs and the difficulties they found in such a design process. The participants were 47 PPTs, working in groups of 2 or 3, forming 19 groups in total. The data source for analysis was the report written by each group. The oral presentation of these reports in class also served to clarify any doubts about the models elaborated by the PPTs. The models were analysed and categorized using qualitative content analysis methods, by combining inter- and intra-rater evaluation strategies. The results reveal that PPTs in general used a variety of resources to make models about the water molecule. Nonetheless, they found it harder to model the differences between the three aggregation states of water from a molecular perspective. The PPTs also acknowledged having had difficulties, such as when choosing and handling the materials they used to create the models or when thinking how to adapt them for the explanations to their peers. It is concluded with a discussion and implications of this study towards the PPTs' training in scientific modelling and its didactics.