The document discusses various causes of water pollution in the European Union. It states that water pollution is caused by both natural factors like acid rain and human factors such as oil spills, vehicle emissions, bacteria, pesticides, waste from treatment plants, and industrial discharges. It also discusses how water pollution has led to diseases spreading globally, using the example of schistosomiasis caused by a parasite from contaminated water. Pesticides are highlighted as a major human-caused pollutant that can be toxic to both animals and humans. The document emphasizes that water is the most important resource and calls for efforts to preserve it from pollution.