What does "stormwater runoff" refer to?

Stormwater runoff specifically refers to water that comes from precipitation events—such as rain or melting snow—that flows over surfaces rather than being absorbed into the ground. This phenomenon occurs when the intensity of rainfall exceeds the rate at which the soil can absorb the water, or when surfaces are impermeable, like roads and buildings.

This runoff can carry pollutants into streams, rivers, and lakes, thus contributing to water quality issues and erosion. Understanding this concept is essential for stormwater management, as it emphasizes the importance of controlling and managing runoff to protect local ecosystems and water resources.

Other options, while related to water management, do not accurately define stormwater runoff. For instance, water that is absorbed by the ground is part of the hydrological cycle but not considered runoff. Similarly, filtered water through drainage systems is already treated in some manner, and water stored in reservoirs for agriculture is not associated with the natural runoff process following a precipitation event.