--- title: "Factors affecting water demand; variation" subject: "Water Supply Engineering" chapter: 3 key: "semester_5/water_supply_engineering:factors-affecting-demand" source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/factors-affecting-demand site: BCT Engineering --- # Factors affecting water demand; variation Water Supply Engineering · Chapter 3: Quantity of Water - Asked in: 2072 Chaitra, 8 marks; 2068 Baisakh (old course), 8 marks; 2066 Jestha (old course); 2066 Bhadra (old course); 2067 Asar (old course) (asked 5 times) - Video: [1.3.1.4 Factors Affecting Water Demand | CE602 |](https://www.youtube.com/watch?v=VEcHG784VEs) — RGPV Official - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/factors-affecting-demand - Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-3 ## Question Describe the factors affecting the rate of water demand and the variation of (hourly) water demand. (How is the peak demand calculated?) ## Short answer Climate, community size, living standard, industrial activity, water quality, pressure, tariff, supply system and losses all affect demand. Demand varies seasonally (higher in summer), daily (max daily ≈ 1.8 × average) and hourly (peak ≈ 2.7 × average). Peak hourly = 1.5 × max daily; distribution mains are designed for this peak. ## Answer #### Factors affecting the rate of demand 1. **Climate:** Hot and dry weather increases the use of water for drinking, bathing, cooling and gardening. 2. **Size and type of community:** Large cities use more water per head than villages; industrial or commercial cities use more. 3. **Standard of living:** Rich households with flush toilets, baths and appliances use much more than poor households. 4. **Industrial and commercial activities:** Factories, hotels, and offices raise the demand. 5. **Quality of water:** Better and safer water encourages use. 6. **Pressure in the distribution system:** High pressure increases consumption and leakage. 7. **Cost (tariff) and metering:** Metered supply and higher tariff reduce wastage; flat rate and free taps increase it. 8. **System of supply:** Continuous supply uses more water than intermittent supply. 9. **Water loss and wastage:** Leaky pipes and careless use increase demand. 10. **Other:** Habits and culture, availability of sewerage, and fire demand. #### Variation of demand - **Seasonal variation:** Demand is highest in summer (about 1.1 to 1.2 times the average) and low in winter. - **Daily variation:** Higher on holidays, hot days and during festivals; maximum daily demand is about 1.8 times the average daily demand. - **Hourly variation:** Demand is low at night and high in the morning (6 to 9 am) and evening (5 to 8 pm). The peak hour demand is about 1.5 times the maximum daily demand, or 2.7 times the average. ```text Demand | /\ /\ | / \ / \ | / \____/ \ |___/ \___ 0 6 12 18 24 hour (morning & evening peaks) ``` #### Peak demand Peak factors are applied to the average daily demand $Q_{avg}$: - Maximum daily demand $= 1.8\,Q_{avg}$ (Nepal rural: about 1.5) - Peak hourly demand $= 1.5\times$ maximum daily demand $\approx 2.7\,Q_{avg}$ (population 20,000 to 50,000: factor about 2.0 to 3.0 in Nepal practice). The distribution mains are designed for the peak hourly demand, while the source and transmission main are designed for the maximum daily demand. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does metering with tariff affect demand? A. It increases wastage B. It reduces wastage compared to flat rate or free taps C. It has no effect D. It raises leakage Answer: B. Metered supply and higher tariff reduce wastage. (Key point: Cost and metering) 2. Which supply system leads to higher consumption? A. Intermittent supply B. Rationed supply C. Continuous supply D. Supply through stand posts only Answer: C. Continuous supply uses more water than intermittent supply. (Key point: Supply system) 3. What is the peak hour demand in terms of the maximum daily demand? A. 1.5 times B. 1.8 times C. 2.7 times D. 1.1 times Answer: A. Peak hourly = 1.5 x maximum daily, about 2.7 x average. (Key point: Peak hour demand) 4. Which demand is used to design the distribution mains? A. Average daily demand B. Peak hourly demand C. Minimum demand D. Seasonal minimum Answer: B. Distribution is designed for peak hourly; source and transmission for maximum daily demand. 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