What is the most common source of contamination for freshwater resources?

Runoff from land surfaces is the most common source of contamination for freshwater resources due to the way water interacts with various materials as it moves over the ground. When rain falls or when snow melts, water flows across land surfaces, picking up pollutants such as fertilizers, pesticides, oil, heavy metals, and other contaminants that are present on the soil or in urban areas. This contaminated runoff then flows into rivers, lakes, and groundwater, significantly impacting water quality and ecosystems.

The prevalence of land use—agricultural, urban, and industrial—contributes to the extent of contamination as these areas often have substances that can easily be washed into bodies of freshwater. Effective management of land and water resources, including practices like buffer strips and proper waste disposal, is vital in mitigating this source of freshwater contamination.

While the melting of glaciers can introduce freshwater into ecosystems, it typically does not contribute contaminants in the same pervasive manner as runoff. Digging wells primarily impacts groundwater levels and distribution, and lightning strikes do not play a significant role in contaminating freshwater sources.