The contamination of water sources is a significant environmental risk associated with improper pesticide use. When pesticides are not applied correctly, they can wash off from treated areas during rainfall or irrigation, leading to runoff that carries these chemicals into nearby water bodies. This not only poses a direct threat to aquatic life but can also affect the quality of drinking water, harming both human health and the environment.
In contrast, the other options, such as increased crop yields, improved soil health, and enhancement of biodiversity, represent potential benefits or neutral outcomes that are typically associated with proper agricultural practices, including the responsible and judicious use of pesticides. However, when pesticides are misused, the negative impacts on water sources supersede any intended beneficial outcomes.