San Bernardino County, CA Environmental Rules: Stormwater Management (2026)

Stormwater regulation in unincorporated San Bernardino County operates under two Municipal Separate Storm Sewer System (MS4) permits issued by the Santa Ana Regional Water Quality Control Board (southwestern valley area) and Lahontan Regional Water Quality Control Board (desert and mountain areas) pursuant to the federal Clean Water Act and California Water Code 13000+. Construction sites disturbing 1 acre or more require coverage under the statewide Construction General Permit including Storm Water Pollution Prevention Plans (SWPPPs), Best Management Practices (BMPs) for erosion and sediment control, and Qualified SWPPP Developer oversight. Smaller sites may require local BMPs under the county Stormwater Program. Post-construction BMPs such as bioretention, permeable pavement, and infiltration trenches are required for projects over specific size thresholds. Non-stormwater discharges to storm drains are prohibited under County Code including car washing runoff, pool drainage, concrete slurry, and cleaning solvents. Illicit discharge reporting hotline operates 24/7. Failure to comply with MS4 permit can result in fines up to $10,000 per day under Water Code 13350. The County Flood Control District maintains regional stormwater infrastructure and enforces drainage easement protections.