The Shit Flow Diagram: A Tool to Visualize Urban Sanitation Failures
The shit flow diagram (SFD) is a visual tool that maps how human waste moves through urban sanitation systems, using color-coded arrows to distinguish safe from unsafe management. Developed by organizations like the World Bank and the Bill and Melinda Gates Foundation, SFDs reveal hidden sanitation gaps in low- and middle-income countries. In Babati, Tanzania, for example, an SFD showed that 69% of fecal waste is unsafely discharged, prompting local authorities to prioritize fecal sludge management over costly sewer expansion.
The width of each arrow in the diagram proportionally reflects the percentage of the population's excreta represented by that particular flow to communicate the relative scale of safe and unsafe sanitation practices.