Domestic sewage (wastewater) includes:
1) “Black Water” – everything that goes down the toilet or urinal
2) “Greywater” – everything else; from sink, dishwasher, laundry, showers, etc.
There are also organics (proteins, organic material), nutrients (phosphorus, nitrogen,) and pathogens (bacteria, viruses, protozoa, helminths) in sewage. Properly designed soil-based treatment areas will treat and remove most of these elements.