In the face of prevalent water management challenges such as floods and droughts, continuous and widespread observations of weather are of crucial importance to equip at-risk locations with essential information as we have to deal with more frequent and/or more intense cases of these natural hazards. Yet there are two major problems with the traditional means of observing the weather using Remote Sensing (RS) and in-situ observations of meteorological variables: firstly, the low resolution and density of the data acquired using these methods and, secondly, the passive role that they perceive for citizens in terms of understanding their environment. Therefore, increasing attention is being paid to the importance and the potential of 'citizen science' (or citizen observations), coupled with the diffusion of Information Communication Technologies (ICTs) that are interactive and easy to use. ICT-enabled citizen observatories, involving citizens in gathering data and perhaps even higher levels of active participation in governance and decision making processes, can provide new means to face natural hazards and the water supply and wastewater operations challenges resulting from them. Nevertheless, their success hinges on the continued involvement of citizens as central actors of these initiatives and developing strategies to (further) engage them requires in-depth understanding of the behavioural determinants that encourage or impede individuals to collect and share weather-related data. In this research, the behavioural determinants of sharing personally-collected weather data via webplatforms have been analyzed using the Theory of Planned Behavior from the behavioural sciences. The findings and analysis are based on a qualitative empirical research carried out in three EU-member countries, complemented by a review of secondary material and relevant literature. In total, 30 interviews were conducted and 43 online questionnaires completed in the Netherlands, the United Kingdom and Italy covering two major group of ...