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Caltrans water pollution control manuals provide direction on how to prepare a Storm water Pollution Prevention Plan (SWPPP) and Water Pollution Control Program (WPCP).

Most storm drains simply collect rain water and channel it away to prevent flooding, carrying polluted runoff to local water resources. Sanitary sewers carry wastewater or “sewage” from homes and businesses through an entirely separate piping network below city streets.

Unable to soak into the ground, stormwater quickly flows or floods downstream from developed land during the rainy season. As a result, floods can damage homes and businesses, flood septic system drain fields and overwhelm streams, wetlands and wildlife habitat.

Stormwater and irrigation runoff from gardens and lawns, car washing, etc., runs down the streets via gutters into the storm drains. The runoff flows through pipes into regional ponding basins and either infiltrates into groundwater or discharges into creeks, canals or the San Joaquin River.

Water that flows down driveways and streets and into a gutter goes into a storm drain which flows directly to a lake, river or the ocean. This water may pick up pollutants along the way which are never treated.

Wastewater, or sewage, comes from drains and toilets in homes and businesses. It's treated at a wastewater treatment plant before being released back into a waterway. Stormwater is rain water that does not soak into the ground.