Stormwater runoff occurs when precipitation from rain or snowmelt flows over the ground. Impervious surfaces like driveways, sidewalks and streets prevent stormwater from naturally soaking into the ground. Stormwater can pick up debris, chemicals, dirt and other pollutants and flow into a storm sewer system or directly to a lake, stream, river, wetland, or coastal water. Anything that enters a storm sewer system is discharged untreated into the waterbodies used for swimming, fishing and providing drinking water. The Orange County Soil and Water Conservation District has a lot of useful information and tips and tools to help reduce stormwater runoff. One exciting project is their Storm Drain Marking Program which includes eye-catching disks that are glued to storm drain inlets to remind people that "only rain should go down the drain". Education is the key to help the public better understand the cause and effect of stormwater runoff. Some tips include implementing low-impact development and Better Site Design.
The Orange County Department of Planning webpage hosts a number of documents including Annual MS4 Reports.