Water supply engineering is one of the most critical branches of civil engineering — ensuring safe, adequate, and reliable drinking water is a public health imperative. India has 1.4 billion people; despite major investments under Jal Jeevan Mission (JJM) and AMRUT, millions still lack piped water supply. For civil engineers, water supply design spans hydrology, hydraulics, treatment processes, and distribution network engineering.
Water Demand
Per Capita Daily Demand — IS 1172:1993
| Category | Per Capita Demand (litres/person/day) |
|---|---|
| Village (JJM standard minimum) | 55 LPCD |
| Small towns (<20,000 population) | 100–150 LPCD |
| Medium towns (20,000–100,000) | 150–200 LPCD |
| Cities (100,000–1,000,000) | 200 LPCD |
| Metropolitan (>1 million) | 200–400 LPCD |
| IS 1172 desirable (with full facilities) | 200 LPCD |
Components: Domestic (50%), industrial (30%), institutional (5%), losses/NRW (15–20%)
Population Forecasting Methods
Design period: 30 years (IS 1172). Forecasting methods:
| Method | Formula | Best For |
|---|---|---|
| Arithmetic progression | P_n = P₀ + n × X̄ (X̄ = avg annual increase) | Slow, uniform growth areas |
| Geometric progression | P_n = P₀ × (1 + r)^n | Rapidly growing cities |
| Incremental increase | P_n = P₀ + n × (arithmetic mean) + n(n+1)/2 × (mean increment of increments) | Moderate growth |
| Logistic curve | P = P_sat / (1 + m × e^(−kn)) | Saturating urban populations |
| Regression / Trend analysis | Census data fit | Long-term planning |
Sources of Water Supply
Surface Water Sources
- Rivers (intake works — drum screen, bar screen, jack well)
- Lakes and reservoirs (storage dams)
- Tanks and ponds (traditional; Rajasthan, AP)
Groundwater Sources
- Open wells (ring wells) — shallow; not hygienic for public supply
- Borewells / tube wells — deep aquifer; most rural water supply in India
- Springs and infiltration galleries
Water Treatment Process
Full treatment train for surface water (IS 10500 compliance):
- Screening: Bar and drum screens remove large debris
- Plain sedimentation: Removal of heavy particles by gravity (2–4 hr detention)
- Coagulation: Alum (Al₂(SO₄)₃) or FeSO₄ added to destabilise colloids; dose = 10–30 mg/L
- Flocculation: Gentle stirring (G × t ≈ 10⁴–10⁵) forms large, settleable flocs
- Sedimentation (Clariflocculator): 2–4 hr detention; horizontal velocity < 0.3 m/min; overflow rate 12–18 m³/m²/day
- Filtration (Rapid Sand Filter): 600 mm sand layer, rate 5 m³/m²/hr; backwashing 12–15 m/hr for 10–15 min when head loss exceeds 3 m
- Disinfection: Chlorination — residual chlorine 0.2 mg/L at consumer end; contact time × concentration (CT) = 0.2 mg/L × 30 min = 6 mg·min/L
- Fluoridation: In areas with <0.6 mg/L natural fluoride; add to 0.8 mg/L (IS 10500 maximum 1.0 mg/L)
Slow Sand Filtration vs Rapid Sand Filtration
| Parameter | Slow Sand Filter (SSF) | Rapid Sand Filter (RSF) |
|---|---|---|
| Filtration rate | 0.1–0.4 m/hr | 5–10 m/hr |
| Sand size | 0.15–0.35 mm (effective size) | 0.45–0.75 mm |
| Cleaning | Scraping top 25–50 mm (biannual) | Backwash daily/2-daily |
| Pre-treatment needed | No (if turbidity <10 NTU) | Yes (coagulation-sedimentation) |
| Area required | Large (25× more than RSF) | Compact |
| Cost | Low (no chemicals) | Higher (chemicals + energy) |
| Best for | Small towns, rural (RWSS) | Large cities (MPWSS, TWAD) |
IS 10500:2012 — Drinking Water Quality Standards (Key Parameters)
| Parameter | Desirable Limit | Maximum Permissible |
|---|---|---|
| Turbidity (NTU) | 1 | 5 |
| pH | 6.5–8.5 | No relaxation |
| TDS (mg/L) | 500 | 2000 |
| Hardness (CaCO₃, mg/L) | 200 | 600 |
| Fluoride (mg/L) | 1.0 | 1.5 |
| Nitrate (mg/L) | 45 | — |
| Arsenic (mg/L) | 0.01 | — |
| Iron (mg/L) | 0.3 | — |
| Residual chlorine (mg/L) | 0.2 min. | 1.0 |
| E. coli / faecal coliform | Absent in 100 mL | — |
Distribution System Design
Types of Distribution Systems
| Type | Description | Advantage | Limitation |
|---|---|---|---|
| Dead End / Tree System | Branches from main with dead ends | Simple, low cost | No circulation; stagnation; unreliable supply |
| Grid (Ring) System | Interconnected loops; no dead ends | Reliable; less NRW; easy isolation | Higher capital cost; complex analysis |
| Circular / Ring Main | One ring serving entire area | Uniform pressure; resilient | Large pipe sizes needed |
| Radial System | Central reservoir; radial distribution | Gravity-fed; simple | Uneven pressure at extremities |
Hardy-Cross Method for Pipe Network Analysis
The Hardy-Cross method iteratively solves for pipe flows in a closed network:
- Assume flows in all pipes (satisfy continuity at each node: ΣQ_in = ΣQ_out)
- Calculate head loss in each loop: h_f = r × Q^n (r = pipe resistance, n = 1.85 for Hazen-Williams)
- Calculate correction: ΔQ = −ΣhL / (n × Σ|hL/Q|)
- Apply correction to flows; repeat until ΔQ < 0.001 m³/s (or negligible)
Non-Revenue Water (NRW)
NRW = water produced − water billed. India's urban NRW averages 35–50% (international target: <15%).
Components: Physical losses (leakage from pipes, joints) + Commercial losses (illegal connections, meter errors)
Reduction by: District Metered Areas (DMA), pressure management, GIS-based network mapping, 100% metering.
Frequently Asked Questions
What is the maximum permissible turbidity for drinking water as per IS 10500?
IS 10500:2012 specifies 1 NTU as the desirable limit and 5 NTU as the maximum permissible limit for turbidity in drinking water. WHO guideline is <1 NTU for safety. High turbidity indicates suspended particles that may harbour pathogens and interfere with disinfection effectiveness — this is why filtration must reduce turbidity to <1 NTU before chlorination.
What is the Jal Jeevan Mission and what does it mean for water supply engineers?
Jal Jeevan Mission (launched 2019) aims to provide every rural household with a functional household tap connection (FHTC) by 2024 — a target of 19 crore connections. This is the largest water supply programme in world history by scale. It has created enormous demand for civil engineers skilled in rural water supply schemes (RWSS): intake works, overhead tanks, distribution networks, and treatment plants for small-to-medium settlements.