Design a standpipe by comparing the peak draw of the households it serves with what one tap can pass: at 0.33 liters per second a tap delivers 1,188 liters an hour, about 800 liters an hour once buckets are swapped, so a tap serving 8 households at 250 liters a day each, with a peak of 208-250 liters an hour, is roughly a quarter to a third used, while a tap serving 30 households is overloaded. The pipe to the standpipe must also pass the flow of every tap that can run at once and leave at least 5 meters of head at the spout.
Part of Community Water System
Standpipe design is the sizing of a communal tap stand: how many taps, at what height, on what pad, fed by what pipe, so that queues stay short and the water arrives with usable pressure.
A Tap Is A Server With A Finite Rate, And Queues Form When Peak Demand Passes It
The community water system page sets the rule of one standpipe for every 5-8 households within 200 m of each home, each with a tap and a drained pad. That rule gives a head count per tap. This page tests it against the flow: how much water the households want in the busy hour, and how much one tap can deliver. If the first exceeds the second, a queue grows every morning and evening however good the pad is.
Peak demand is not the average. Distribution Network takes the peak hour at 2.5-3 times the average hourly demand, because most water is drawn in the morning and evening.
What You Need
- Household count per standpipe and per-household use
- A tap rate, measured with a bucket and a watch
- The time lost per bucket change, measured at an existing tap
- The pipe’s residual head at the stand (Head Calculation)
Method: Compare Peak Draw With Tap Capacity
Step 1: Daily draw = households × persons per household × liters per person.
Step 2: Average hourly draw = daily draw ÷ 24.
Step 3: Peak hourly draw = average hourly × 2.5 to 3.
Step 4: Tap capacity per hour. A tap running at Q liters per second delivers Q × 3,600 L/h. Subtract time lost swapping containers: with a bucket of 20 L and a swap time you measure.
Step 5: Utilisation = peak draw ÷ capacity. The lower it is, the faster a queue clears; as it approaches 1 the queue lengthens through the whole busy period, and above 1 it cannot clear until demand falls.
Step 6: If overloaded, add a second tap on the same stand or another standpipe, rather than raising the flow.
Worked Example: Eight Households Against Thirty
Inputs: 5 people per household and 50 L per person per day (assumptions); tap flow 0.33 L/s from a 20 L bucket filling in 60 s; 30 s to swap buckets (assumed).
- Per household: 5 × 50 = 250 L/day.
- Tap capacity, no swapping: 0.33 × 3,600 = 1,188 L/h.
- With swapping: each 20 L bucket takes 60 + 30 = 90 s, so 3,600 ÷ 90 = 40 buckets an hour = 800 L/h.
Eight households: 8 × 250 = 2,000 L/day. Average = 2,000 ÷ 24 = 83.3 L/h. Peak = 83.3 × 2.5 = 208 L/h up to 83.3 × 3 = 250 L/h. Utilisation = 208 ÷ 800 = 26% up to 250 ÷ 800 = 31%.
Thirty households: 30 × 250 = 7,500 L/day. Average = 312.5 L/h. Peak = 781 to 938 L/h. Utilisation = 781 ÷ 800 = 98% up to 938 ÷ 800 = 117%. The tap is saturated at best and overloaded at worst; the queue builds all peak hour.
Flow needed in the pipe: each tap that can run at once adds 0.33 L/s, so a stand with two taps asks for 0.66 L/s (Pipe Sizing). Adding a second tap to the thirty-household stand halves the utilisation but doubles the pipe flow.
Tap Height, Pad And Surge
The standpipe-construction page puts the spout 50 cm above a pad of 1.5 m × 1.5 m sloped 2% away from the tap (Standpipe Construction). Choose the spout height by the tallest container used. A ball valve that is closed fast can surge a line by about 3 bar (Tap Types), which a rigid pipe feels most, so a self-closing or slow-closing tap is kinder to the pipe but breaks more often.
Failure Modes
- Queue grows each peak: utilisation near or above 1; add a tap or a stand.
- Trickle at the spout: residual head too low, friction too high, or an upstream valve half shut.
- Tap leaks all night: a worn washer wastes water; flow out of the tank at night with every tap closed is the sign (Leak Detection).
- Standing water on the pad: the fall or the drain has failed (Drainage Pads).
Common Mistakes
- Sizing taps to the daily total. The peak hour governs.
- Counting the free-flow rate and ignoring bucket changes. It overstates capacity by about half (1,188 against 800).
- Adding taps without checking the pipe. More open taps lower the pressure at every tap.
Safety
Surge, wet concrete and freezing
Close the valve upstream before working on a tap, and release the pressure first. Wet cement burns skin and eyes. In frost, drain the riser or protect it, because a split riser floods the pad (Frost Protection).
What’s Next
- Learn next: Drainage Pads — keeping the stand clean and dry
- Combine with: Water Committee — who maintains the taps and enforces use