What are the primary sources of pollutants in storm water run-off?

The primary sources of pollutants in storm water run-off are varied, but spills of products on the ground represent a significant and immediate source of contamination. When products such as oil, chemicals, or fertilizers are accidentally spilled, they can wash away into storm drains during rainfall or snowmelt. This direct transfer of harmful substances into the water system poses risks to both aquatic ecosystems and human health.

Considering the other contexts, while rainwater collection itself does not introduce pollutants, the contamination can occur when rainwater collects over areas where spills have happened, but that is more about transportation rather than the source. Construction sites are known to contribute pollutants as well, primarily through sediment and debris that can wash off during rain, but they typically focus more on solid materials than liquid pollutants. Agricultural runoff is indeed a significant source of nutrients and pesticides, but the focus on "spilled products" encompasses a wider variety of potential pollutants, making it a more direct answer in the context of specific incidents that introduce contamination into storm water systems.