What is a non-point source?

• A. A pollutant discharge from a single pipe
• B. Storm water discharge
• C. A direct air emission
• D. A landfill leakage

Answer: (B)

Non-point sources are diffuse, coming from many small sources spread over a wide area rather than from one identifiable outlet. Storm water discharge fits this idea because rainwater picks up pollutants as it flows over many surfaces—roads, lawns, and soils—and carries them into waterways. This broad, cumulative input is what defines a non-point source.

In contrast, a pollutant discharge from a single pipe is a point source—there’s one clear outlet to the environment. A direct air emission isn’t a water pollution source, so it doesn’t describe a water non-point source. Landfill leakage can be localized to the site, which is more like a point source; the storm water runoff example is the classic non-point source.