Wastewater treatment system/pathway usage often differs for rural and urban residents. Also, in developing
countries, there are likely to be differences between urban high-income and urban low-income residents. Hence,
a factor U is introduced to express each income group fraction. It is good practice to treat the three categories:
rural population, urban high income population, and urban low income population separately. It is suggested to
use a spreadsheet, as shown in Table 6.5 below.