For the design of sewers in India, the percentage of sewage discharge is assumed as
- A25-30% of water supplied from waterworks
- B50-70% of water supplied from waterworks
- C75-80% of water supplied from waterworksCorrect
- D100% of water supplied from waterworks
Solution
Concept
Design sewage discharge percentage of water supply
Formula
NONE
Step-by-step solution
1. Not all water supplied to a community returns to the sewer system due to consumption and losses. 2. In standard Indian practice, a major portion of supplied water converts to municipal wastewater. 3. Therefore, the percentage of sewage discharge for sewer design in India is assumed as 75-80% of water supplied from waterworks. Answer: C
Explanation
In standard Indian engineering practices, it is assumed that not all supplied water reaches the sewerage system due to losses like lawn watering, washing, and evaporation. Therefore, sewer capacity is calculated assuming 75% to 80% of the total municipal water supply converts into sewage flow.
Why the other options are wrong
A) 25-30% is significantly lower than the standard sewage conversion percentage. B) 50-70% underestimates the typical sewage generation rate in Indian urban design. D) 100% overestimates sewage flow as water is consumed, evaporated, or lost in system leakage.
Shortcut
Sewage discharge design assumption = 75% to 80% of water supplied.
Common mistake
Underestimating the design sewage flow percentage relative to the total water supplied.
Correct answer: C) 75-80% of water supplied from waterworks