Design a shared water supply in a fixed order: work out daily demand, measure the source’s dry-season flow, check the height of the source above the taps, size the pipe, storage and taps, and decide who maintains it before anything is dug. For 20 people with a garden and some livestock, plan for 1,500-2,500 liters a day; a spring that gives 0.5 liters a minute in August supplies only 720 liters a day, so the dry-season flow, not the spring-time flow, decides whether the design works.
Part of Community Water System
System design is the planning stage of a gravity-fed community water supply: the order in which demand, source, height, pipe, storage and taps are fixed so that each decision sets the limits of the next.
Each Decision Sets The Limits Of The Next, So The Order Is Fixed
A water system built from the source downward, or from whatever pipe happens to be on hand, tends to fail in the one month nobody measured. Design from the people backward instead. Demand tells you how much water is needed; the source tells you how much exists in the worst month; the height tells you what pressure is free; only then does it make sense to choose pipe, because pipe size is a response to flow and head and not a starting point.
| Step | Question | Settled by |
|---|---|---|
| 1 | How many liters per day? | Demand Calculation |
| 2 | Which source, and what does it give in the worst month? | Source Selection |
| 3 | Is there enough height to use gravity? | Gravity-Fed Systems |
| 4 | What pipe, and how is it joined? | Pipe Materials |
| 5 | Where do people collect it? | Distribution Points |
| 6 | Who keeps it running? | Maintenance and Governance |
What You Need
- A head count and a list of uses — people, animals, garden area
- A flow measurement of the source in its driest month — see Source Selection
- A height survey from the source water level to the highest tap you want to serve
- A treatment and testing plan — a spring is not automatically safe
Method: Design Backward From The Dry Season
Step 1: Fix demand. The carrier figures are a minimum of 20 liters per person per day, and 50-80 liters for a comfortable community with laundry and a garden. Add livestock and irrigation separately.
Step 2: Measure the source in its worst month. Time a known container filling. If the worst-month flow is below demand, no pipe or tank cures that; storage only moves water between hours of the same day or between wet and dry weeks.
Step 3: Compare and decide. If the dry-season flow covers the comfortable demand, design for it. If it covers only the minimum, design for the minimum and plan a backup (Dry Season Backup) and rules for use.
Step 4: Check the height. About 10 meters of drop gives about 1 bar. The least-pressured tap needs at least 0.5 bar (5 m of head) after friction, and no pipe section should carry more than 60 m (about 6 bar) of static head (Head Calculation).
Step 5: Size the pipe to the flow and the head left after the 5 m minimum (Pipe Sizing).
Step 6: Size storage at no less than one day’s supply, then place the standpipes.
Step 7: Treat, test and assign upkeep before the first household relies on it (Water Treatment at Scale, Community Water Testing).
Worked Example: Twenty People In A Dry August
Inputs: 20 people; spring flow 5 liters per minute in April and 0.5 liters per minute in August (the carrier’s example).
- Comfortable demand for people alone: 20 × 50 = 1,000 L/day up to 20 × 80 = 1,600 L/day. Livestock and a garden bring the total to the carrier’s 1,500-2,500 L/day.
- Spring in April: 5 L/min × 1,440 min = 7,200 L/day. Ample.
- Spring in August: 0.5 L/min × 1,440 min = 720 L/day.
- Basic need in August: 20 people × 20 L = 400 L/day. The August flow covers that with 320 L/day to spare.
- Shortfall against the comfortable total in August: 1,500 - 720 = 780 L/day up to 2,500 - 720 = 1,780 L/day.
The design therefore works at the minimum all year and at the comfortable level only outside the dry season. That is a usable result, and it is knowable before a trench is dug. Storage of one day’s supply is 1,500-2,500 L; it smooths daily peaks but cannot make up an 780-1,780 L/day gap that lasts weeks.
Common Mistakes
- Designing to the spring-time flow. The system then runs dry in the month it is needed most.
- Choosing pipe first because it is available. Too small a bore loses the head you needed at the tap.
- Forgetting that one system feeds everyone. A single contamination event reaches every household at once.
- Leaving upkeep to “whoever notices”. Systems with no assigned maintainers fail within about two years, per the carrier.
Safety
One shared supply can sicken a whole community at once
Everyone drinks from the same source, so a single contamination event, such as an animal carcass uphill of the intake or a cross-connection, reaches every household. Treat the water, test it on a schedule, and keep any non-drinking line physically separate from the drinking line. Test new pipe with water, never compressed air, because plastic pipe can shatter and throw fragments.
What’s Next
- Learn next: Demand Calculation — the first number every other number depends on
- Combine with: Pipe Sizing — turning flow and head into a pipe diameter