Why one type of water pollution can be pinned to a single pipe and permitted with a numeric limit — and why the other, despite being the bigger problem in most watersheds, structurally can't be regulated the same way.
Both terms describe pollution reaching a waterway, but the distinction between them is not cosmetic — it determines which regulatory tool even applies. Point source pollution is discharged from a single, identifiable, discrete conveyance — a specific pipe outfall, a specific ditch, a specific channel — with a clearly traceable origin. Because it comes from one specific, identifiable location, it can be directly measured, monitored, and regulated right at that point. Nonpoint source pollution does not come from any single identifiable point at all. It originates from diffuse, widespread sources spread across a large land area, carried into waterways primarily by rainfall and snowmelt runoff flowing over and through the landscape — and there is no discrete location where a monitoring device or a numeric limit could even be applied.