What does the term "drainage fixture unit" (DFU) quantify?

The term "drainage fixture unit" (DFU) quantifies the load that a plumbing fixture contributes to the drainage system. This measurement is essential for understanding how different fixtures impact the overall capacity and performance of the drainage system. Each fixture has a specific DFU value that reflects the expected amount of wastewater it generates and how frequently it will contribute to the drain flow.

By using DFUs, plumbing engineers and inspectors can accurately assess the total load on a drainage system, allowing for appropriate sizing of pipes and ensuring that the system can handle peak usage without risk of clogs or overflow. This method also helps in designing systems that comply with building codes and standards related to drainage.

Other options, such as the capacity of a water heater, pressure within the water supply line, and the size of individual plumbing fixtures, while relevant to plumbing systems, do not pertain to the specific function of DFUs in measuring drainage load.