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Sanitation · Understand your wastewater · sanitation-1Learn the wastewater streams
Household wastewater splits into streams with very different risks and uses. Knowing them lets you decide which to treat together, which to separate and which to reuse.
How
- Blackwater: toilet water carrying faeces and urine. It holds most of the pathogens and nitrogen and always needs full treatment.
- Greywater: water from showers, baths, basins and laundry. In homes with flush toilets it is roughly 60% of all wastewater, holds far fewer pathogens and only 10 to 20% of the nitrogen of blackwater (Eawag Compendium).
- Kitchen sink and dishwasher water: rich in grease and food solids. Some codes (for example California) exclude it from greywater reuse, so treat it with blackwater unless your local rules say otherwise.
- Urine on its own: the main nutrient stream, low in pathogens if kept free of faeces. It can be collected separately with a urine-diverting toilet.
- Write down which rooms and fixtures produce each stream in your planned house.
Sources
- Compendium of Sanitation Systems and Technologies (1st edition). Eawag-Sandec, accessed 2026-11
- Use of Graywater in Urban Landscapes. University of California Cooperative Extension, accessed 2026-11