Size the services that are buried or hard to change, such as water mains, wells, foundations and path widths, for the final population, and add the easy ones, such as barrels, bins and benches, as the settlement grows. A 50 mm main carries about 1.0 L/s, while the peak demand of 300 people at 30 L per person a day is only about 0.3 L/s, so the pipe is rarely the limit and the water source, the storage and the hall are.
Part of Settlement Layout for 150 People
Infrastructure scalability is the design of a settlement’s water, sanitation, fire and building services so that they can serve a larger population without being rebuilt.
Fixed Services Scale In Steps, Movable Ones Scale In Units
Digging a trench twice costs more than laying a larger pipe once. That asymmetry decides which services to build for the final load. The test for each service is: how costly is it to change after it is buried, poured or built around? If changing it is costly, size it for the end state; if cheap, scale it with the population.
Worked Example: Water
Inputs: basic service 30 L per person a day and a peak-hour factor of 2.5-3 (both from the distribution guide); pipe capacities from the same guide: 50 mm about 1.0 L/s, 75 mm about 3.0 L/s (Distribution Network).
- Daily demand at 150 people: 150 × 30 = 4,500 L; at 300 people: 9,000 L.
- Average flow = daily demand ÷ 86,400 s: 4,500 ÷ 86,400 ≈ 0.052 L/s; 9,000 ÷ 86,400 ≈ 0.104 L/s.
- Peak flow = average × 2.5 to 3: 0.13-0.16 L/s at 150 people; 0.26-0.31 L/s at 300 people.
- Compare with 1.0 L/s: the peak flow of 300 people is about 0.3 L/s, so a 50 mm main carries three to four times that.
So the pipe does not need to change within the layout guide’s population, and the water system is limited instead by what the source yields in the dry season and by storage (Community Water System). The distribution guide’s table matches 50 mm to 100-200 people, and the arithmetic above shows headroom beyond that, so flow is not the first constraint; pressure limits (30 m maximum head) can force pressure zones before flow does (Water Distribution Routes).
Worked Example: Buildings And Fire Water
Inputs: gathering hall guide’s meeting allowance of 1.0-1.5 m² per person and dining allowance of 1.5-2.0 m²; the fire guide’s at-least 5,000 L for 150 people.
- Meeting space for 150 people: 150 × 1.0 = 150 m² to 150 × 1.5 = 225 m². The hall guide sizes 100-150 m² for 100 people, so 150 people exceed a hall sized for 100.
- Seated dining for 150: 150 × 1.5 = 225 m² to 150 × 2.0 = 300 m², more than a 150-200 m² footprint, so dining runs in two sittings.
- Fire water scaled in proportion: 5,000 L for 150 is about 33 L per person, so 300 people suggests about 10,000 L. That is a linear extension, an assumption and not a figure from the fire guide.
What You Need
- The final-population target (and the margin above it)
- A list of services with a cost-to-change for each
- Source yield data for the dry season
Method: Sort Each Service
Step 1: List every service: mains, wells, tanks, hall, kitchen, latrines, paths, fire water.
Step 2: Mark buried or built-around services and size them for the end state.
Step 3: Mark modular services and scale them with headcount: composting toilets at one per household, barrels at one per cluster.
Step 4: Find the limiting resource — usually source flow, not pipe size.
Step 5: Re-test at each phase.
Common Mistakes
- Sizing the main for today only and digging again within two years.
- Over-sizing a well pump or tank that the source cannot fill.
- Ignoring the population cliff at 150, where hall, kitchen and governance all need to change shape.
Safety
Overloaded sanitation fails first
If the population outgrows sanitation capacity, contamination reaches water within a season. Add toilets and compost capacity before adding people, and keep the separation from water sources whatever the crowding (Source Protection).
What’s Next
- Learn next: Community Gathering Hall — the building that most visibly outgrows its plan
- Combine with: Expansion Corridors — the land growth will use