Greywater

Wastewater categories matter because the category determines what you can legally do with the water. Three terms come up most often:

• Greywater is wastewater from baths, showers, bathroom sinks, clothes washers, and laundry tubs. It contains soap, hair, skin, and detergent residue but not human waste. In California, Chapter 16 of the Plumbing Code allows on-site greywater reuse for subsurface irrigation under specific permitting conditions.
• Blackwater is wastewater from toilets, urinals, kitchen sinks, and dishwashers — anything with fecal matter, food waste, or pathogen load. Blackwater goes to the sanitary sewer or to a permitted septic system. It cannot be reused on-site under residential or most commercial occupancy classifications.
• Process water (sometimes called industrial wastewater) is the wastewater generated by an industrial or commercial process — pressure-washing runoff, food-plant wash-down water, vehicle wash-bay water, manufacturing rinses. It has its own regulatory framework, typically discharged to the sanitary sewer under an industrial pretreatment permit if it exceeds local sewer discharge limits.

Where does pressure-washing runoff sit? It’s process water. Not greywater, not blackwater. The contamination profile varies job-by-job — a sidewalk wash collects sediment and detergent; a dumpster pad wash collects organic matter, grease, and hypochlorite; a parking deck wash collects hydrocarbons, brake dust, and tire rubber. None of that is reusable, and none of it can legally go to a storm drain under California’s MS4 framework.

The right disposal channel depends on what’s in the water. Most commercial pressure-wash runoff in San Diego is discharged at a contractor’s shop sanitary sewer connection, sometimes after on-truck filtration to remove gross solids. Heavily contaminated loads — significant hydrocarbon content, for example — may need to be hauled as regulated waste to a licensed treatment facility, though this is rare for routine commercial work.