Sizing Pump Capacity to Sphere Water-Point Standards

Q: What is a pump duty point?

One flow at one head, for example 12 cubic metres per hour at 75 metres. Total dynamic head is the pumping water level plus the discharge height plus friction losses in the rising main.

Tony Miller
Aug 20
6 min read

Sphere caps a camp tapstand at 250 people, based on a flow of 7.5 litres per minute over an eight-hour collection day. That works out to 3,600 litres per tap and 14.4 litres per person, just under Sphere's own 15-litre minimum. Size the pump above the ratio, not to it.

What does Sphere actually require, and what does it quietly assume?

The Sphere Handbook water supply standard 2.1 sets a minimum of 15 litres per person per day for drinking and domestic hygiene, a maximum of 250 people per tap at 7.5 litres per minute, 500 people per hand pump at 17 litres per minute, and 400 people per open hand well at 12.5 litres per minute, with the nearest water point under 500 metres from any household and queuing under 30 minutes.

The assumption underneath those ratios is the part people skip: Sphere states the minimum quantity targets assume the water point is accessible for about eight hours a day of constant supply. Tap counts, storage volume and pump duty all follow from that window.

How do you get from camp population to daily demand?

Four inputs, in this order.

Litres per person per day. The IFRC summary of the Sphere WASH standards breaks the 7.5 to 15 litre band into 2.5 to 3 litres of intake, 2 to 6 litres of hygiene and 3 to 6 litres of cooking, which is survival, not service. WHO Technical Note No. 9 puts the minimum for essential health and hygiene nearer 20 litres per capita per day, and UNHCR plans displacement water supply on 20 litres per person per day excluding leakage. Design to 20. A scheme sized at 15 is at its ceiling on day one.

Institutional demand. Sphere Appendix 3 gives 5 litres per outpatient per day, 40 to 60 litres per in-patient, 3 litres per pupil, and 60 litres per patient plus 15 per carer in a cholera treatment centre. Health posts and schools sit on the same pipe as the tapstands, and are usually left out of the sum.

System losses. Leakage, tank cleaning, flushing and overflow. Fifteen per cent is a defensible allowance, to be checked against metered readings once the system runs.

Contingency. Uganda hosted 2,036,021 refugees and asylum seekers as of 31 July 2026 on Office of the Prime Minister and UNHCR figures, and settlement populations move faster than boreholes get drilled.

Why does the Sphere tap ratio undershoot the litres standard?

Do the arithmetic. A tap at 7.5 litres per minute for eight hours delivers 3,600 litres a day. Split across Sphere's maximum of 250 people, that is 14.4 litres each, below the 15-litre minimum in the same standard. The hand pump holds up better: 17 litres per minute for eight hours is 8,160 litres, or 16.3 litres each across 500 people. The open hand well lands exactly on the line, 6,000 litres and 15 litres each across 400 people.

The tap ratio is the weak one, and it is the one most schemes are built on. At 20 litres per person per day, the same 3,600 litres supports 180 people, not 250. Use 180 as the planning figure and treat 250 as the ceiling for the first weeks of an influx.

Worked example: a 10,000-person settlement zone

Step 1, domestic demand. 10,000 people at 20 litres per person per day is 200,000 litres, or 200 m³ per day.

Step 2, institutional demand. A health centre with 20 in-patients at 50 litres each is 1,000 litres. Eighty outpatients at 5 litres each is 400 litres. Schools with 1,200 pupils at 3 litres each is 3,600 litres. Total 5,000 litres, or 5 m³ per day.

Step 3, subtotal and losses. 200 + 5 = 205 m³ per day. Add 15 per cent for losses: 205 × 0.15 = 30.75 m³. Design demand is 235.75 m³ per day, rounded up to 236 m³ per day.

Step 4, tapstands. At 180 people per tap, 10,000 ÷ 180 = 55.6, so 56 taps. Those 56 taps deliver 56 × 3,600 = 201,600 litres across the eight-hour window, which covers the 200 m³ of domestic demand with a thin margin. Site them so no household walks more than 500 metres.

Step 5, pumping hours. Storage decouples the pump from the collection window, so the pump need not match the taps hour for hour. On a motorised scheme, ten hours of pumping leaves time for daily checks and a fuel or grid interruption. 236,000 litres ÷ 10 hours = 23,600 litres per hour, or 23.6 m³ per hour.

Step 6, sources. If the yield test returns a safe sustainable yield of about 12 m³ per hour per borehole, two production boreholes are needed: 2 × 11.8 m³ per hour × 10 hours = 236 m³ per day. One borehole cannot do it, and no pump will change that.

Step 7, storage. Hold at least one full day of demand so a pump failure does not become a distribution failure. Two Oxfam T95 tanks and one T70 give 95 + 95 + 70 = 260 m³, comfortably above the 236 m³ design demand.

How do you turn the flow figure into a pump duty point?

A duty point is one flow at one head. Take the per-borehole flow of 11.8 m³ per hour and build the total dynamic head from the site survey: pumping water level 60 metres below ground at the test rate, a tank inlet 8 metres above ground, and friction loss along the rising main read off the pipe manufacturer's chart, say 6 metres for a 250-metre run. That is 74 metres, rounded to a duty of 12 m³ per hour at 75 metres.

The hydraulic power then follows: 1,000 × 9.81 × (12 ÷ 3,600) × 75 = 2,452 watts, about 2.45 kW at the water. At a wire-to-water efficiency of 55 per cent, that is roughly 4.5 kW of input power, a conventional four-inch submersible.

Run the same duty on solar and the window shrinks to the useful solar day. Seven hours instead of ten raises the per-borehole flow from 11.8 to 16.9 m³ per hour, so pump and array both grow and the storage carries the night. The World Bank's Solar Pumping: The Basics still finds solar cost-competitive with diesel across all size ranges and about 36 per cent cheaper over the life cycle, against a diesel borehole scheme spending more than US$5,000 a year on fuel alone.

What if the arithmetic exceeds the borehole yield?

Add a source, not a bigger pump. A pump specified above the aquifer's sustainable yield pulls the water level down to the intake, breaks suction, cycles on its low-level cut-out and cooks the motor while the tapstands still run dry at midday. The population arithmetic sets the target, the yield test sets the ceiling, and the pump is chosen last, to sit near its best-efficiency point at the calculated duty.

Where the yield will not stretch, the options are another borehole, a surface source with treatment, or trucking as a bridge. All three cost less than a burnt motor and a dry camp. SLS supplies borehole and dewatering pump equipment with in-country installation, commissioning and yield testing, including across Uganda's refugee settlements, so the duty point on the order matches the borehole it will sit in.

Frequently asked questions

How much water per person per day should I size a camp pump for?

Size for 20 litres, not 15. Sphere's 15 litres is a minimum, while UNHCR plans displacement water supply on 20 litres per person per day excluding leakage and WHO Technical Note No. 9 puts the minimum for essential health and hygiene nearer 20 litres per capita per day.

How many taps does a camp of 10,000 people need?

Fifty-six, at a planning figure of 180 people per tap. A tap at Sphere's assumed 7.5 litres per minute over an eight-hour day delivers 3,600 litres, which is 20 litres each for 180 people. Sphere's maximum of 250 people per tap yields only 14.4 litres each.

How many hours a day should a borehole pump run?

Ten hours for a motorised scheme, leaving time for checks and interruptions, and about seven for solar. Sphere's ratios assume the tapstand is accessible for about eight hours a day of constant supply; storage is what lets the pumping window differ from the collection window.

What is a pump duty point?

One flow at one head, for example 12 m³ per hour at 75 metres. Total dynamic head is the pumping water level plus the discharge height plus friction losses in the rising main.

Does a cholera outbreak change the sizing?

Yes, upwards. Sphere Appendix 3 allows 60 litres per patient per day plus 15 litres per carer in a cholera treatment centre, and household demand rises with handwashing and laundry, so build the headroom into storage and sources rather than the pump alone.