The principle difference between point source and nonpoint source water pollution is .

b. the number of sources of pollution

Explanation:

The U.S. Environmental Protection Agency (EPA) describes the point source pollution as “any particular identifiable cause of pollution from which pollutants are released, such as a channel, ditch, boat or factory chimney”. Factories and sewerage treatment of plants are two well-known types of point sources.

The distinction between the point and non point source pollution is that point cause of pollution which has a single origin or source while non point source pollution is a combination of pollutants from various origins, and not all of them are easily identified.