In general, domestic wastewater entering municipal wastewater systems tend to follow a diurnal
pattern (Asano et al. 1985). This flow is low during the early morning hours and a first peak
generally occurs in the late morning followed by a second peak in the evening—after dinner hour.
However, the ratio of peak flow loads to average flow is likely to vary inversely with the size of
the community and the length of sewer system. Peak flows may also be generated during festive
occasions, and at times of religious rituals, such as the Friday prayer in Pakistan, during business
hours, tourist seasons, and in areas with large university campuses etc.
Industrial wastewater flows, closely follow the processing pattern of local industries, which
depend on the processes involved, the number of shifts operated, and the water requirement of
the industry. Variations from established patterns are minimal and occur during shift changes or
stoppages. Flow variations may also occur due to processing of seasonal products. Therefore,
seasonal fluctuations in the industrial wastewater discharges are more significant. In cities where,
industrial wastewater constitutes a major component of the total municipal wastewater flow,
fluctuations in industrial wastewater discharges are likely to be of significant importance in water
cycle management.
In developed economies, per capita wastewater generation is largely determined by economic
factors and reliability of water supply. However, in a developing country like Pakistan, where
water supplies are rationed, availability is uncertain, and since water is not priced at its true
opportunity cost, per capita wastewater generation may largely be a function of availability and
minimum usage requirements.