What is the difference between point source and nonpoint source water pollution?

Hint: Point source pollution refers to the pollution that occurs from a single identifiable source while nonpoint source pollution refers to the pollution that occurs via many diffuse sources. The discharge of effluents occurs at one point in point source pollution while the discharge of effluents over a wide area leads to nonpoint source pollution. This is the main difference between point source and nonpoint source pollution.

Complete answer:
Point source pollution: any single identifiable source of pollution from which pollutants are discharged, such as a pipe, ditch, ship or factory smokestack. This untreated, polluted water then runs directly into a sewer system.
Nonpoint source pollution: nonpoint source pollution can include: Excess fertilizers, herbicides and insecticides from agricultural lands and residential areas. Oil, grease and toxic chemicals from urban runoff and energy production. Sediment from improperly managed construction sites, crop and forest lands, and eroding stream banks
The United States Environmental Protection Agency defines point source pollution as any contaminant that enters the environment from an easily identified and confined place. Nonpoint-source pollution is the opposite of point-source pollution, with pollutants released in a wide area.

Note:
We can solve non-point pollution by managing animal waste to minimize contamination of surface water and groundwater. Protect drinking water by using less pesticides and fertilizers. Reduce soil erosion by using conservation practices and other applicable best management practices. Use planned grazing systems on pasture and rangeland.