1. Concept Explanation (Exam-Focused)
Sewerage Flow is the quantity of wastewater
flowing in a sewer system per day, originating mainly from water
supplied to the population.
In SSC JE / RRB JE, questions are highly numerical
and test:
- Relation
between water demand and sewage flow
- Peak
factor application
- Components
like infiltration & inflow
📌 Golden Exam Concept:
Sewerage flow ≈ 70–85% of water demand
Components of Sewerage Flow
- Domestic
Sewage – From residential water use
- Industrial
Sewage – Depends on industry type
- Infiltration
– Groundwater entering sewers
- Inflow
– Rainwater entering through manholes
⚠ Trap: Infiltration ≠
Inflow (frequently asked)
2. Important Formulas (Highly Repeated)
1️⃣ Average Sewage Flow
Where:
= Sewage flow (MLD)
= Water demand (MLD)
2️⃣ Per Capita Sewage Flow
Where:
= Per capita water demand
(LPCD)
3️⃣ Maximum Sewage Flow
Where:
Peak factor 
4️⃣ Minimum Sewage Flow
🧠 Mnemonic Trick:
“Water × 0.8 → Sewage → × Peak”
3. Short Notes / One-Liners (Last-Day Revision)
✔ Sewage flow is always less
than water demand
✔ Design of sewers is based on maximum flow
✔ Infiltration is unavoidable
✔ Inflow can be controlled by proper design
✔ Peak sewage flow occurs morning & evening
4. PYQ Patterns (SSC JE / RRB JE)
🔹 Conversion of LPCD →
MLD
🔹
Applying 0.8 factor directly
🔹
MCQs on difference between infiltration & inflow
🔹
Peak factor misuse (2 vs 3)
⚠ Typical Trap:
Students use fire demand in sewage calculations (❌)
5. Solved Examples
Example 1 (Numerical – SSC JE Level)
Population = 40,000
Water demand = 135 LPCD
✅ Answer: Average
sewage flow = 4.32 MLD
Example 2 (Maximum Sewage Flow)
Peak factor = 2.5
6. MCQs (Exam Level – 30 Questions)
1. Sewerage flow is approximately what % of water supply?
A) 50%
B) 60%
C) 70–85%
D) 100%
✅
Ans: C
2. Which component adds groundwater to sewers?
A) Inflow
B) Leakage
C) Infiltration
D) Runoff
✅
Ans: C
3. Fire demand contributes to sewerage flow:
A) Fully
B) Partially
C) Indirectly
D) Not at all
✅
Ans: D
4. Peak factor for sewer design is generally taken as:
A) 1
B) 1.5
C) 2–3
D) 5
✅
Ans: C
5. Minimum sewage flow is about:
A) Equal to average
B) Half of average
C) Double of average
D) Zero
✅
Ans: B
6. Inflow mainly enters through:
A) Pipes
B) Soil
C) Manholes
D) Pumps
✅
Ans: C
7. If per capita water demand is 150 LPCD, per capita
sewage flow is:
A) 150
B) 120
C) 100
D) 80
✅
Ans: B
8. Sewers are designed for:
A) Average flow
B) Minimum flow
C) Maximum flow
D) Fire flow
✅
Ans: C
9. Which is TRUE?
A) Sewage flow > water demand
B) Inflow is unavoidable
C) Infiltration is unavoidable
D) Peak factor < 1
✅
Ans: C
10. Average sewage flow is generally taken as what
fraction of water supply?
A) 0.5
B) 0.6
C) 0.8
D) 1.0
✅
Answer: C
📝
Explanation: 70–85% ≈ 0.8 × water demand
11. Which of the following DOES NOT contribute to sewage
flow?
A) Domestic water use
B) Industrial wastewater
C) Fire demand
D) Infiltration
✅
Answer: C
📝
Trap: Fire demand never enters sewers
12. If per capita water demand is 135 LPCD, per capita
sewage flow is approximately:
A) 90 LPCD
B) 100 LPCD
C) 108 LPCD
D) 135 LPCD
✅
Answer: C
📝
Calculation: 0.8 × 135 = 108 LPCD
13. Peak sewage flow usually occurs during:
A) Midnight
B) Early morning & evening
C) Noon only
D) Night only
✅
Answer: B
14. Infiltration in sewers is mainly due to:
A) Rainwater runoff
B) Leakage from water mains
C) Groundwater entry
D) Industrial discharge
✅
Answer: C
15. Inflow differs from infiltration because inflow is:
A) Groundwater
B) Continuous
C) Rain-dependent
D) Unavoidable
✅
Answer: C
16. Which factor is used to obtain maximum sewage flow?
A) Fire factor
B) Peak factor
C) Safety factor
D) Return factor
✅
Answer: B
17. Typical value of peak factor for sewer design is:
A) 1–1.5
B) 1.5–2
C) 2–3
D) 4–5
✅
Answer: C
18. A town has population 25,000 and water demand 135
LPCD. Average sewage flow is:
A) 2.7 MLD
B) 3.0 MLD
C) 3.375 MLD
D) 4.0 MLD
✅
Answer: A
📝
Calculation:
Water = 25,000 × 135 = 3.375 MLD
Sewage = 0.8 × 3.375 = 2.7 MLD
19. Minimum sewage flow is approximately:
A) Equal to average
B) 0.75 × average
C) 0.5 × average
D) Zero
✅
Answer: C
20. Sewer design capacity is based on:
A) Average flow
B) Minimum flow
C) Maximum flow
D) Fire flow
✅
Answer: C
21. Which statement is TRUE?
A) Sewage flow > water demand
B) Inflow is unavoidable
C) Infiltration is unavoidable
D) Peak factor < 1
✅
Answer: C
22. Industrial sewage contribution mainly depends on:
A) Population
B) Climate
C) Type of industry
D) Rainfall
✅
Answer: C
23. If average sewage flow is 5 MLD and peak factor is 3,
maximum flow is:
A) 5 MLD
B) 7.5 MLD
C) 10 MLD
D) 15 MLD
✅
Answer: D
24. Which component can be reduced by proper sewer
maintenance?
A) Domestic sewage
B) Industrial sewage
C) Infiltration
D) Inflow
✅
Answer: D
📝
Explanation: Inflow can be controlled; infiltration is unavoidable
25. Sewage flow calculations generally exclude:
A) Industrial wastewater
B) Domestic sewage
C) Fire demand
D) Infiltration
✅
Answer: C
26. If water demand is 10 MLD, sewage flow will MOST
LIKELY be:
A) 5 MLD
B) 6 MLD
C) 8 MLD
D) 10 MLD
✅
Answer: C
27. Unit commonly used for sewage flow in design
calculations is:
A) LPCD
B) L/min
C) MLD
D) m³/s
✅
Answer: C
28. Peak factor depends mainly on:
A) Rainfall
B) Population size
C) Pipe diameter
D) Soil type
✅
Answer: B
29. Which statement is INCORRECT?
A) Sewage flow is less than water supply
B) Fire demand contributes to sewage
C) Infiltration adds extra flow
D) Peak factor > 1
✅
Answer: B
30. For small towns, peak factor is generally:
A) Lower
B) Zero
C) Higher
D) Equal to 1
✅
Answer: C
📝
Explanation: Smaller population → higher variation → higher peak factor
Last-Minute JE Memory Trick 🧠
“Sewage = Water × 0.8 | Design = Max Flow | Fire = ZERO |
Infiltration stays”