Q1: It is customary to design a sewer for D.W.F. on the basis of

ANS:C - thrice the average demand

Designing a sewer system for thrice the average demand means that the capacity of the sewer system is calculated to handle flow rates that are three times the average flow rates observed during dry weather conditions (D.W.F.). Designing for thrice the average demand provides a significant safety margin and ensures that the sewer system can accommodate unexpected peaks in flow, such as during heavy rain events, sudden surges in water usage, or potential future increases in population or industrial activity. By designing for thrice the average demand, engineers aim to prevent overflow, backups, or other system failures during periods of high flow. This approach enhances the reliability and resilience of the sewer system, reducing the likelihood of flooding, pollution, and other adverse impacts on public health and the environment. While designing for thrice the average demand increases construction costs and may result in a larger infrastructure footprint, it provides a robust and long-lasting solution that can effectively handle varying flow conditions and accommodate future growth and development.