Large streams of open data become available on a daily basis and are expected to support a number of public bodies and water authorities in their safety policies and strategies. At the European level, more than 2.5 million of Sentinel-1A products are published online from the European Space Agency, corresponding to 3 million GB of data and 350,000 products. Copernicus data have already paved the way to monitor changes on Earth, using Sentinel data, aiming at efficient and emergency management services and protection of critical infrastructure. Open weather forecast data are also available from meteorological institutes, adopting the full, free and open access policy of the Copernicus programme. In our tool, these two main sources of weather and satellite data are supported by citizen observations, as they are reporting short messages, images and spatiotemporal information on social media platforms, such as Twitter. Our technologies involve water body detection from satellite data, event detection from the available sources of data and their positioning on a map when spatiotemporal information is available or automatically estimated. Concepts are extracted from satellite or social media images and topics are created by grouping similar Twitter posts. Furthermore, our tool automatically identifies whether an image refers to a flood or not, using computer vision state-of-the-art techniques, based on deep convolutional neural networks. Our tool also offers animation of the user communities to identify authorities in the social network of user interactions. The extracted knowledge is represented in a semantic way that allows for generating notifications and making decisions in an effective and efficient way. These technologies are very useful for water authorities and civil protection agencies in their need to monitor a flood event and to have a holistic view of an area at the preparedness, response and recovery stages.