Water Pipeline & Distribution Design

Engineering water from the well to the user — pipe sizing, pressure management, storage, and network design.

Table of Contents

Distribution System Types
Pipe Sizing
Pressure Zone Design
Storage Tank Design
Hydraulic Calculations
Water Loss Management

Distribution System Types

Type	Description	Best For	Cost
Dead-end (tree)	Branching from main — no loops	Small communities, linear settlements	Lowest
Grid (loop)	Interconnected network — multiple paths	Towns, urban areas	Medium
Radial	Central source → radiating mains	Hilly terrain, elevated storage	Medium
Combined	Grid core + dead-end branches	Most real-world systems	Variable

Pipe Sizing

Hazen-Williams Equation:
V = 0.849 × C × R^0.63 × S^0.54
V = velocity (m/s), C = roughness coefficient, R = hydraulic radius (m), S = hydraulic gradient

Pipe Diameter Selection:
D = √(4Q / πV)
D = pipe diameter (m), Q = flow rate (m³/s), V = velocity (m/s)
Target velocity: 0.6-1.5 m/s (minimize friction + prevent sedimentation)

Pipe Diameter	Flow Capacity	Velocity (typical)	Common Use
50 mm (2")	0.5-1.5 L/s	0.5-1.0 m/s	House connections
75 mm (3")	1.5-4 L/s	0.6-1.2 m/s	Small service lines
100 mm (4")	4-10 L/s	0.7-1.3 m/s	Street mains
150 mm (6")	10-25 L/s	0.8-1.4 m/s	Distribution mains
200 mm (8")	25-50 L/s	0.9-1.5 m/s	Transmission mains
300 mm (12")	50-120 L/s	1.0-1.5 m/s	Large transmission

Pressure Zone Design

Target pressure: 20-60 m head (2-6 bar) at service connections
Minimum pressure: 10 m head (1 bar) — required for fixtures to function
Maximum pressure: 80 m head (8 bar) — prevents pipe damage and leakage
Pressure zones: Divide system into zones by elevation — each zone 30-40 m range
Pressure reducing valves: Install at zone boundaries — prevent over-pressurization

Storage Tank Design

Sizing Criteria

Daily storage: 1-2 days of average demand — provides buffer for pump outages
Fire storage: Additional 1-4 hours of peak flow for fire protection (if required)
Emergency reserve: 24-72 hours for power failures and emergencies

Tank Volume:
V = Q_peak × T_buffer
V = tank volume (m³), Q_peak = peak hourly demand (m³/hr), T_buffer = buffer time (hours)

Elevated Tank Height:
H = P_required / (ρ × g) + Z_min
H = tank height above lowest service point (m), P = required pressure (Pa)

Tank Types

Type	Capacity	Height	Cost	Best For
Elevated steel	10-500 m³	20-40 m	High	Towns, pressure zones
Ground-level concrete	50-10,000 m³	3-8 m	Medium	Large communities
Bolted steel	10-500 m³	3-10 m	Medium	Modular, relocatable
Bladder tank	1-50 m³	Ground	Low	Temporary, emergency
Hypertank	100-5,000 m³	Ground	Medium	Large community storage

Hydraulic Calculations

Friction loss: Use Hazen-Williams or Darcy-Weisbach — account for pipe roughness, fittings, valves
Minor losses: Bends, tees, valves — typically 10-30% of total friction loss
Nodal analysis: Software models (EPANET, WaterGEMS) solve network hydraulics
Peak factor: Multiply average demand by 1.5-3.0 for peak hourly flow
Fire flow: Add fire demand (10-30 L/s) to normal demand for sizing

Water Loss Management

Non-revenue water: Typical 20-50% in developing countries — water produced but not billed
Real losses: Leakage from pipes, joints, and fittings — physical water loss
Apparent losses: Metering inaccuracies, unauthorized use — billing losses
District metered areas (DMAs): Divide network into zones — measure flow in/out to identify losses
Leak detection: Acoustic correlation, step-testing, pressure management
Target: Developed countries: <10% NRW | Developing: <25% NRW

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Pipe Material Selection

HDPE (PE100): Flexible, corrosion-proof, fused joints — best for most applications. PVC: Rigid, lower cost,brittle in cold. Ductile iron: Strong, high pressure — best for transmission mains. Steel: Highest strength — for high-pressure and large-diameter applications.