Distribution Network

Part of Water Systems

How to design and build a piped water distribution network serving multiple households from a single source.

Why This Matters

Moving water from a single source to many users is one of the highest-leverage investments a community can make. It eliminates the daily labor of water carrying — typically borne by women and children — frees time for productive work, reduces waterborne disease by separating human settlement from water sources, and enables sanitation infrastructure that would otherwise be impossible.

A distribution network does not require complex materials. Communities across the developing world have built functioning gravity-fed piped water systems from clay pipe, bamboo, or basic iron pipe using only hand tools and local labor. The engineering requirements are understood well enough that a small team with basic surveying skills and arithmetic can design and build a system that will serve a village for decades.

The key design decisions are: where to draw water, how much head (pressure) is available, how to size pipes for adequate flow, and how to distribute water fairly among many users. Each of these is tractable with simple tools and principles.

Network Types

Branching network: A single main pipe from the source splits into progressively smaller branches serving individual taps or households. Simple to design, but any break in the main disables all downstream users.

Ring main (looped network): The main supply pipe forms a loop around the served area, with branches feeding off the loop. Flow can reach any point from two directions — one section can be repaired while the rest of the system stays live. More pipe is required, but reliability is much higher.

Gravity-fed vs. pumped: Always use gravity if a source exists above the served area. Even a few meters of head difference can supply a functional system. Pumped systems require energy and mechanical reliability that are difficult to sustain in a rebuilding scenario.

Intermittent supply: Design for the possibility that water flows only during certain hours (controlled from a valve at the source). This reduces pipe sizing requirements and allows smaller storage tanks to compensate for demand peaks.

Demand Estimation

Before designing the network, know how much water it must deliver.

Use Level	Liters per person per day
Survival minimum	3–5
Basic hygiene	15–20
Comfortable household	30–50
Small livestock included	50–100

Peak demand factor: Daily demand is not evenly distributed. Most water is drawn in the morning and evening. The peak hour demand is typically 2.5–3× the average hourly demand. Size pipes for peak flow, not average.

Example: Village of 200 people, 30 L/person/day basic service.

• Total daily demand = 200 × 30 = 6,000 liters = 6 m³/day
• Average hourly = 6,000 / 24 = 250 L/hour = 0.07 L/s
• Peak hour = 0.07 × 2.5 = 0.175 L/s = 175 mL/s (about 10.5 L/min)
• Source must yield at least 6 m³/day; pipes sized for 0.175 L/s peak

Hydraulic Design: Pipe Sizing

Water flow in pipes is governed by the Hazen-Williams equation (approximate, but accurate enough for design):

V = 0.849 × C × R^0.63 × S^0.54

Where V = velocity (m/s), C = pipe roughness coefficient, R = hydraulic radius (= diameter/4 for full pipe), S = head loss per meter of pipe.

For practical design, use the head loss formula: Head loss h = (10.67 × L × Q^1.85) / (C^1.85 × D^4.87)

Where h = head loss (m), L = pipe length (m), Q = flow (m³/s), C = Hazen-Williams C, D = pipe diameter (m)

Hazen-Williams C values:

• New cast iron or clay: 130
• Old cast iron: 100
• Concrete: 120
• Bamboo or wood: 80–100

Simplified pipe sizing table (flow in L/s, velocity target 0.5–1.5 m/s):

Pipe ID	Max flow (L/s)	Notes
25 mm	0.2	Single household branch
38 mm	0.5	Small cluster (5–10 houses)
50 mm	1.0	Village main (100–200 people)
75 mm	3.0	Town main (500–1000 people)
100 mm	6.0	Town distribution (2000+ people)

Design rule: The available head minus friction losses in the main must leave at least 1–2 meters of residual pressure at every user point. Less than 1 meter means water barely trickles from taps; more than 30 meters means joints and taps are overstressed.

Layout Planning

1. Map source and users: Draw to scale. Mark elevations at key points.
2. Identify the hydraulic grade line: From source (100% head available) to the lowest-pressure tap (0% residual). The slope of this line must be steeper than the pipe friction gradient.
3. Place the service reservoir: Ideally 10–20 meters above the highest user point. The reservoir provides storage for demand peaks and buffers supply variations.
4. Route the main: Follow topography to avoid air locks (high points in the pipe). If high points are unavoidable, install air release valves.
5. Plan branch taps: Each household branch should be 20–25 mm diameter with a stopcock at the branch connection.
6. Identify wash-out points: At low points in the network, install scour valves so the system can be drained and cleaned.

Air Locks and Pressure Considerations

Air in pipes: Air trapped at high points blocks flow completely. Vent air by:

• Routing pipes to avoid high points where possible
• Installing automatic air release valves (a small float-controlled valve that opens when air is present, closes when water arrives)
• Bleeding air manually at system start-up by cracking a joint at the high point until water emerges steadily

Surge pressure (water hammer): Rapid valve closure creates pressure spikes that can crack pipes and burst joints. Avoid fast valve closure. Always open and close valves slowly (30+ seconds for full travel). Install surge tanks or standpipes at vulnerable points in large systems.

Pressure reduction: If the source is very high above users (50+ meters), the pressure at low-lying taps becomes destructively high. Insert a break-pressure tank — an open tank that breaks the hydraulic grade line — and restart the distribution from the tank at a lower head. One or more break-pressure tanks may be needed on steep terrain.

Construction Sequence

1. Survey the route — establish elevations at pipe alignment points
2. Dig trenches — 450 mm minimum depth, route as mapped
3. Lay and joint pipes — working from source downward
4. Install valves and taps — at branches, ends, and low/high points
5. Backfill and mark — mark pipe locations with surface markers for future maintenance
6. Fill and test — open source slowly, check all joints for leaks before burying
7. Flush the system — run water until clear before connecting to households
8. Train operators — at least two people per community should understand valve operation, how to isolate sections, and how to repair joints

Management and Maintenance

A water network requires ongoing management or it fails within years. Establish:

• A maintenance committee with responsibility for the system
• A simple fee from users to fund consumables (pipe repair, gaskets)
• A written record of the network layout, valve locations, and pipe sizes
• Annual inspection of all visible components — source intake screen, break-pressure tanks, service reservoir, exposed pipes, taps
• A repair kit — extra pipe sections, gasket material, valve packing, basic hand tools

The most durable water systems in low-resource settings are those owned and maintained by the communities they serve, not those installed by outside organizations with no local investment.