In the City of Los Angeles, there are two systems of drainage. The Sanitary Sewage, or Wastewater System (left), and the Storm Drain System (right).

The Wastewater Sewage System takes household wastewater (such as sinks, toilets, washers,etc.) and carries it through a home’s plumbing and into an underground sewer pipe.

On the other hand, and as seen in the graphic below, the Storm Drain System carries discharge off of city streets and routes it into curb side catch basins. From there, it also enters another underground, but completely separate system.

Street surface runoff enters the underground stormdrain system.
Household Wastewater enters the Sanitary Sewer System