1. Concept Explanation (Exam-Focused)
Water Demand is the total quantity of water
required per capita per day for all purposes in a community.
In SSC JE / RRB JE exams, questions are usually direct,
formula-based, or statement-oriented.
Types of Water Demand
- Domestic
Demand – Drinking, cooking, bathing (largest share)
- Industrial
Demand – Depends on type of industry
- Public
Use Demand – Schools, hospitals, parks
- Fire
Demand – Asked directly in numericals
- Losses
& Wastage – Leakage, theft (10–20%)
📌 Exam Focus:
✔ Per capita demand values
✔ Fire demand formulas
✔ Peak factors
✔ Unit conversions (MLD ↔ LPCD)
2. Important Formulas (Highly Repeated)
1️⃣ Per Capita Demand
$$q = \frac{Q}{P}$$
Where:
q = Per capita demand (LPCD)
Q = Total daily water supply (L/day)
P = Population
2️⃣ Total Water Demand
$$Q = P \times q$$
3️⃣ Fire Demand Formulas (VERY
IMPORTANT)
🔥 Kuichling’s Formula
(Most Asked)
$$Q = 3182 \sqrt{P}$$
🔥 Freeman’s Formula
$$Q = 1136 \left( \frac{P}{5} + 10 \right)$$
🔥 Buston’s Formula
$$Q = 5663 \sqrt{P}$$
🧠 Mnemonic:
“KFB – Know Fire Before exam”
3. Short Notes / One-Liners (Last-Day Revision)
✔ Standard per capita demand
in India = 135 LPCD
✔ Domestic demand ≈ 50–60%
of total demand
✔ Fire demand is independent of daily demand
✔ Leakage allowance = 10–20%
✔ Peak hourly demand = 1.5–2.7 × average
4. PYQ Patterns (SSC JE / RRB JE)
🔹 Fire demand formulas
appear every 2–3 years
🔹
Units confusion: L/min vs m³/day (major trap)
🔹
Questions on per capita demand values
🔹
MCQs based on incorrect statements
⚠ Typical Trap:
Population given in thousands, formula needs actual population
5. Solved Examples
Example 1 (Numerical – SSC JE Level)
Population = 50,000
Per capita demand = 135 LPCD
✅ Answer: 6.75 MLD
Example 2 (Fire Demand – Conceptual)
Using Kuichling’s Formula
6. MCQs (Exam Level – Water Demand)
MCQ Set (30 Questions)
- Standard
per capita water demand in India is:
A) 100 B) 135 C) 150 D) 200
✅ Ans: B – CPHEEO standard - Largest
component of water demand is:
A) Industrial B) Fire C) Domestic D) Losses
✅ Ans: C - Unit
of fire demand is:
A) LPCD B) MLD C) L/min D) m³/hr
✅ Ans: C - Kuichling’s
formula depends on:
A) Area B) Population C) Rainfall D) Pressure
✅ Ans: B - Leakage
allowance usually considered is:
A) 5% B) 10–20% C) 30% D) 50%
✅ Ans: B
6. Per capita demand is
expressed in:
A) m³/day
B) L/min
C) LPCD
D) MLD
✅
Answer: C
📝
Explanation: Per capita demand = Litres Per Capita Per Day (LPCD)
7. If population doubles, fire
demand (Kuichling) will:
A) Double
B) Become half
C) Increase by √2 times
D) Remain same
✅
Answer: C
📝
Explanation: Fire demand ∝ √P
8. Which demand is independent
of daily water consumption?
A) Domestic
B) Industrial
C) Fire
D) Public
✅
Answer: C
📝
Explanation: Fire demand depends only on population
9. Standard per capita demand
recommended by CPHEEO is:
A) 90 LPCD
B) 110 LPCD
C) 135 LPCD
D) 150 LPCD
✅
Answer: C
10. Fire demand is generally
expressed in:
A) m³/day
B) LPCD
C) L/min
D) MLD
✅
Answer: C
11. Losses in water
distribution are mainly due to:
A) Evaporation
B) Leakage & theft
C) Fire demand
D) Storage
✅
Answer: B
12. Domestic demand constitutes
approximately:
A) 20–30%
B) 30–40%
C) 50–60%
D) 70–80%
✅
Answer: C
13. If per capita demand is 135
LPCD, total demand for 10,000 population is:
A) 0.135 MLD
B) 1.35 MLD
C) 13.5 MLD
D) 135 MLD
✅
Answer: B
📝
Explanation:
Q = 10,000 × 135 = 1,350,000 L/day = 1.35 MLD
14. Peak hourly demand is
usually:
A) Equal to average
B) Less than average
C) 1.5–2.7 times average
D) 5 times average
✅
Answer: C
15. Which formula gives the
minimum fire demand value?
A) Kuichling
B) Freeman
C) Buston
D) All equal
✅
Answer: A
📝
Explanation: Kuichling gives the lowest estimate
16. Industrial water demand
mainly depends on:
A) Climate
B) Population
C) Type of industry
D) Rainfall
✅
Answer: C
17. 1 MLD is equal to:
A) 1000 L/day
B) 10⁶ L/day
C) 10⁵ L/day
D) 10³ m³/day
✅
Answer: B
18. A town has population
40,000. Using Kuichling’s formula, fire demand ≈
A) 18,000 L/min
B) 20,100 L/min
C) 25,000 L/min
D) 30,000 L/min
✅
Answer: B
📝
Explanation:
Q = 3182√40 ≈ 20,100 L/min
19. Which is NOT a component of
water demand?
A) Domestic
B) Industrial
C) Fire
D) Rainwater
✅
Answer: D
20. If losses are taken as 15%,
effective demand is:
A) Less than total demand
B) Equal to total demand
C) Greater than calculated demand
D) Zero
✅
Answer: C
📝
Explanation: Losses are added to calculated demand
21. Public use demand includes:
A) Factories
B) Schools & parks
C) Houses
D) Fire stations
✅
Answer: B
22. Average daily demand refers
to:
A) Maximum hourly demand
B) Minimum demand
C) Mean of yearly consumption
D) Fire demand
✅
Answer: C
23. If population is given in
thousands, fire demand formula requires:
A) Same value
B) Population in lakhs
C) Actual population
D) Population in millions
✅
Answer: C
📝
Trap Alert: Very common JE mistake
24. Which demand varies the
most during the day?
A) Industrial
B) Fire
C) Domestic
D) Public
✅
Answer: C
25. Burst pipe losses fall
under:
A) Fire demand
B) Industrial demand
C) Losses & wastage
D) Public demand
✅
Answer: C
26. Maximum daily demand is
approximately:
A) Equal to average
B) 1.8 times average
C) 3 times average
D) 5 times average
✅
Answer: B
27. Which statement is TRUE?
A) Fire demand is measured in LPCD
B) Domestic demand is smallest
C) Losses are unavoidable
D) Industrial demand is fixed
✅
Answer: C
28. If per capita demand
increases, total demand will:
A) Decrease
B) Remain same
C) Increase
D) Become zero
✅
Answer: C
29. Which demand is considered
only for design of mains?
A) Domestic
B) Industrial
C) Fire
D) Losses
✅
Answer: C
30. Peak factor is the ratio
of:
A) Average to minimum demand
B) Maximum to average demand
C) Fire to domestic demand
D) Losses to total demand
✅
Answer: B