Sewage is untreated domestic/municipal waste water, which contains mostly of grey water and black water and gets conveyed through the sewerage system or into an onsite sewage facility. Sewage is characterized by its rate of flow, physical condition, chemical and toxic constituents, and its bacteriological status.

Faecal sludge is the mixture of human excreta, water and solid wastes (such as toilet paper and menstrual hygiene materials) that gets collected in onsite sanitation systems.

Septage is a specific type of faecal sludge and refers to the partially digested faecal solids that accumulate in septic tanks. Faecal sludge and septage is emptied out of pits or septic tanks and is much more concentrated than sewage.