Diarrhoeal disease is very common around the world. Often, diarrhoea is caused by pathogenic microorganisms from human faeces and animal manure. Rivers polluted with faeces and manure are an important transmission route. The objective of this thesis is to increase knowledge on the sources, fate and transport of the parasite Cryptosporidium in rivers worldwide using modelling. I present the Global Waterborne Pathogen model for Cryptosporidium (GloWPa-Crypto), the first global model of waterborne pathogen emissions to and concentrations in rivers. The model provides information in regions where little data is available, and it can be used to analyse the relative importance of pollution sources, to study the impact of global change or management strategies, and as a basis to judge disease risk. Knowing more about the global burden of diarrhoeal disease and about the geographical distribution of pathogen pollution is important for decision making and water and sanitation planning.