The SFD describes all of the excreta flows across the city or town, and through all stages of the sanitation service chain. This includes:

• Wastewater from households and institutions which is commonly made up of blackwater, grey water and run off and includes sewage flowing in sewers
• Faecal sludge from onsite sanitation systems
• Excreta deposited directly into the environment via open defecation
• Effluent or supernatant that leaves onsite sanitation systems after solid separation
• Infiltrate, including effluent (or overflow) from onsite sanitation systems that is absorbed by the ground, or discharged.