π’ Updated for 2025 | Complete Notes for Civil Engineering Exams
In the field of Environmental Engineering, a core objective is to ensure a continuous, safe, economical, and efficient water supply that caters to all societal and infrastructural needs. As urbanization increases and population grows, planning and management of water resources becomes even more critical. Effective water supply systems must be designed keeping in mind future projections, sustainability, and environmental safety.
Two major pillars of this domain are:
- Water Demand β Estimating the quantity of water required for domestic, commercial, industrial, institutional, and public uses, including allowances for losses.
- Water Distribution β Designing and operating a reliable infrastructure to deliver this estimated demand to end users at adequate pressure and with minimal loss or contamination.
Together, these components form the foundation for ensuring public health, fire safety, economic development, and quality of life in urban and rural areas.
Letβs understand these topics in detail with exam-oriented insights.
π§ WATER DEMAND IN ENVIRONMENTAL ENGINEERING
β What is Water Demand?
Water demand refers to the total quantity of water necessary to fulfill the needs of a community, including domestic, industrial, commercial, institutional, and public uses. It encompasses not only the actual volume of water consumed but also the inevitable losses due to leakage, wastage, theft, and unaccounted-for uses during transmission and distribution. Effective estimation of water demand is essential for planning, designing, and managing water supply systems, especially in regions with limited resources or rapidly growing populations.
π Categories of Water Demand
| S.No | Type of Demand | Description | Standard Value (LPCD) |
|---|---|---|---|
| 1 | Domestic Demand | For drinking, cooking, washing, bathing, cleaning, etc. | 135 |
| 2 | Industrial Demand | For manufacturing, processing, cooling, and cleaning in factories and workshops | 50 |
| 3 | Commercial Demand | Water used in hotels, restaurants, shops, and office buildings | 20β50 |
| 4 | Public Demand | Water for parks, gardens, fire fighting, road washing, street lighting | 10β20 |
| 5 | Institutional Demand | For schools, hospitals, prisons, military camps, etc. | Varies |
| 6 | Unaccounted Losses | Due to leakages, evaporation, theft, or unmetered connections (also called βNon-revenue waterβ) | 15β20% of total demand |
π§ Factors Influencing Water Demand
| Factor | Effect |
|---|---|
| Climate | Hot, dry areas demand more water for drinking and irrigation |
| Economic Status | Affluent societies consume more due to higher living standards |
| Population Growth | Increases overall demand, especially in urban areas |
| Type of Development | Residential vs industrial β varies significantly |
| Metering & Tariffs | Metered supply discourages wastage, reducing demand |
| Water Pressure | Higher pressure may increase wastage through leakages |
| Seasonal Variation | Higher usage in summer for bathing, cooling, gardening |
π PER CAPITA DEMAND
Definition:
Per Capita Demand (q) is the average amount of water required per person per day.
β««οΈ q = βQ / P
Where:
- q = Per capita demand (LPCD)
- Q = Total water demand (litres/day)
- P = Population
π POPULATION FORECASTING
Accurate population prediction is critical to determine future water needs for proper planning and infrastructure sizing.
== Common Forecasting Methods:
| Method | Formula / Description | Best Use Case |
|---|---|---|
| Arithmetic Increase | Pβ = Pβ + n Γ I | For small towns with stable growth |
| Geometric Increase | Pβ = Pβ Γ (1 + r)βΏ | For fast-growing cities |
| Incremental Increase | Combines Arithmetic + Average increment trend | Medium-growth areas |
| Logistic Curve | S-shaped curve predicting saturation growth | Urban areas nearing population limit |
| Comparative Method | Based on similar towns with known growth | For lack of historical data |
π¦ WATER DISTRIBUTION SYSTEMS
Once water is treated, it must be delivered to consumers efficiently through a strategically designed distribution system. A reliable distribution system ensures:
- π§ Continuous and uninterrupted water supply throughout the day
- π§ Adequate pressure at all consumer outlets, even during peak demand hours
- π‘οΈ Minimal losses due to leakage or theft and protection from any contamination during transit
- π Availability for emergency services such as firefighting
- π Equitable distribution across various zones, irrespective of elevation or distance from the source
π Components of Water Distribution System
- Pipelines (Mains, Sub-mains, Branches)
- Pumping Stations
- Elevated Service Reservoirs (ESRs)
- Valves (sluice, pressure relief, air release)
- Meters for consumption tracking
- Fire Hydrants
π Types of Distribution Systems
| Type | Description |
|---|---|
| Gravity System | Water flows naturally from elevated reservoir. No pumping required. |
| Pumping System | Water is pumped directly; costly and power-dependent |
| Dual System | Separate lines for drinking and other uses (rare in India) |
| Combined System | Mix of gravity and pumping; common in hilly areas or where source elevation varies |
π Distribution Network Layouts
| Layout | Description |
|---|---|
| Dead-End System | Simple tree-like layout. Prone to stagnation. Difficult to maintain. |
| Grid Iron System | Interconnected loops. Ensures continuous supply and easy fault isolation. |
| Radial System | Pipes laid from a central point (like spokes). Used in planned cities. |
| Ring System | Pipes laid in circular loops. Used around cities or large zones. |
π± Storage in Distribution
Water is stored to balance fluctuations in demand and ensure emergency supply. Types:
- Clear Water Reservoirs β at treatment plant
- Service Reservoirs (Overhead Tanks) β for pressure and supply balance
- Underground Storage Tanks β for large volume storage
π FORMULAS IN UNICODE
1. Per Capita Demand:
q = Q Γ· P
2. Total Water Demand:
Q = q Γ P
3. Arithmetic Increase Method:
Pβ = Pβ + n Γ I
4. Geometric Increase Method:
Pβ = Pβ Γ (1 + r)βΏ
5. Fire Demand (Kuchelingβs Formula):
Qf = 3182 Γ βP
6. Freeman’s Formula:
Qf = 1136 Γ ((P Γ· 5) + 10)
7. National Board Formula:
Qf = 4637 Γ βP Γ (1 – 0.01 Γ βP)
8. Average Daily Demand (ADD):
ADD = Total Annual Requirement Γ· 365
9. Max Daily Demand:
Max Daily = 1.8 Γ ADD
10. Peak Hourly Demand:
Peak Hourly = 1.5 Γ Max Daily
π Conclusion
Understanding water demand and water distribution is vital in planning a reliable and cost-effective water supply system. Competitive exams like JKSSB JE Civil, SSC JE, and RRB JE often test these concepts, both theoretically and numerically.
Focus Areas:
- Types of demand and standard values
- Forecasting methods and selection criteria
- System components and network layouts
- IS codes and fire demand formulas
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