The CrowdWater project collects worldwide hydrological data. By using the free CrowdWater app (available for iOS and Android) citizens can collect valuable information about water levels in rivers, streamflow quantities, soil moisture, dynamics of temporary streams, plastic pollution and stream types with simple methods, such as taking pictures of streams and choosing a water level class based on a virtual staff gauge, estimating streamflow (through width, depth and flow velocity) or choosing a qualitative soil moisture class. The collected data will then be evaluated in terms of its use for hydrological modelling by the project team. However, the data is also publicly available for other uses. This approach can be used to improve flood forecasts in regions where otherwise data availability is very limited.