How Much Water Storage Does a Camp Need? Sizing by Population
Camp water storage is population multiplied by the daily litres-per-person target, then increased for reserve, distribution loss and growth headroom, and only then split across tanks. For 10,000 people, Sphere's 15-litre minimum alone puts baseline demand at 150,000 litres a day, before any of that is added.
How do you calculate daily water demand for a camp?
Start with the population you are actually planning for, not the population you counted last month, then multiply by a litres-per-person-per-day target. Two defensible targets exist, and they are not the same number.
Sphere's minimum survival allocation is 7.5 to 15 litres per person per day, covering drinking, cooking and basic hygiene, with a water point no more than 500 metres from the furthest dwelling and a queue no longer than 30 minutes. That is the floor a response is built on, not the target it settles at. Once a site stabilises, UNHCR plans its refugee water supply at 20 litres per person per day, excluding leakage, a figure the WHO also identifies as the minimum needed for essential health and hygiene rather than bare survival.
For a 10,000-person site that gap is not academic. At the Sphere minimum, baseline demand is 10,000 x 15 L = 150,000 litres a day (150 m³). At the UNHCR/WHO figure it is 10,000 x 20 L = 200,000 litres a day (200 m³), and that 200,000 litres still excludes leakage, meaning the real draw on a tank is higher again. Which target you size to should be a deliberate decision recorded in the design, not a default: 15 L/p/d for an initial emergency footprint, moving to 20 L/p/d once storage and distribution catch up.
Why isn't straight daily demand the number you build a tank around?
Because a tank sized to exactly one day's arithmetic average fails in at least four predictable ways.
Treatment contact time removes volume from circulation. Sphere's water-quality standard requires free residual chlorine of at least 0.5 mg/L after 30 minutes' contact time before water is safe to draw. A tank running at its exact daily volume has no room to hold a batch that is still inside that 30-minute window while distribution continues from the rest of the stock.
Collection is not spread evenly across 24 hours. Sphere caps a single tapstand at 250 people, delivering 7.5 litres a minute. Run that flow rate against the same 250 people's 15-litre target and the tap needs to run for roughly eight and a half hours to clear its queue (250 x 15 L = 3,750 L; 3,750 L / 7.5 L per minute = 500 minutes). The tank feeding that tap has to be full at the start of the collection window, not trickle-fed across a full day.
Supply into the tank is not perfectly continuous. A trucking run is missed, a borehole pump loses fuel, a generator fails. Storage is what buys the hours needed to fix that before households breach the 500-metre, 30-minute access standard.
The population itself moves faster than resupply plans. Displacement surges arrive in days, not the weeks a procurement cycle assumes. OCHA recorded roughly 1.4 million people flood-affected across 44 counties and Abyei in South Sudan by late November 2024, with 379,000-plus displaced, and a share of every displacement of that scale lands on sites that already exist. A tank sized to last month's headcount is short by the time the next delivery arrives.
How much reserve should you add, and how do you convert it into tanks?
There is no fixed Sphere figure for reserve capacity; the size of the buffer is an engineering judgement against your own delivery reliability, not a number to copy from a table. What follows is one worked example that shows the method, built for a specific, stated set of assumptions, not a standard to reuse without checking against your own site.
Take the 10,000-person site above, planned at the Sphere minimum of 15 L/p/d.
Baseline. 10,000 x 15 L = 150,000 L/day (150 m³).
Growth headroom. The site is still receiving arrivals and is planned to reach 12,000 within the current reporting period, so it is sized to that figure rather than re-designed every fortnight: 12,000 x 15 L = 180,000 L/day (180 m³).
Interruption reserve. Bulk water arrives by truck on a two-day cycle, so the team holds one full day of demand in reserve to bridge a missed run: +180,000 L.
Total storage target. 180,000 + 180,000 = 360,000 litres (360 m³).
Now convert that target into physical tanks. Oxfam's standard emergency steel tanks come in four sizes: T11, T45, T70 and T95, holding 11, 45, 70 and 95 cubic metres respectively. Four T95 units give 380 m³, covering the 360 m³ target with a small working margin, split across four physical tanks rather than one.
That split is usually the better answer even when a single larger tank could theoretically hold the same volume. One damaged liner or one tank pulled offline for cleaning does not zero out storage if there are three others still standing. Four medium tanks can be sited closer to separate tapstand clusters, shortening the last stretch of hose and keeping more of the camp inside the 500-metre standard. They can also be delivered and commissioned in stages as trucks and plinth-building labour allow, rather than the whole response waiting on one large shipment and one large foundation. A single 380 m³ kit, by contrast, is heavier per unit, needs a bigger flat plinth, and puts the entire site's storage behind one point of failure.
How does site growth change the sizing, and when do you re-size?
Whenever the planning population moves materially, not on a fixed calendar. Treat the calculation as arithmetic to redo, not a one-off design exercise finished at handover. Two triggers matter most in this theatre: sudden displacement, of the kind OCHA's flood snapshots record repeatedly in South Sudan, and outbreak response, where caseload can move faster than a routine population count. Between January and mid-August 2025, South Sudan reported 71,825 suspected cholera cases and 1,194 deaths, a case fatality rate of 1.7%, and an active outbreak of that scale pulls new arrivals into treatment and isolation sites on a timeline no quarterly plan anticipated.
The re-sizing itself is the same three-step chain run again: new population, the litres-per-person target you have chosen, the reserve your delivery reliability requires. What changes is only the inputs, and a design built from several medium tanks rather than one large one makes the answer easier to act on, because adding a fifth tank to a four-tank site is a smaller project than replacing a single undersized one.
As the authorised regional distributor for Oxfam emergency tanks and bladders through Butyl Products UK, SLS holds this tank range in-country in Juba, so a re-sizing decision adds a unit from stock rather than a new import lead time to the response.
Frequently asked questions
How many litres of water storage does a 10,000-person camp need?
At Sphere's minimum of 15 litres per person per day, baseline demand alone is 150,000 litres (150 m³) a day, before any reserve or growth margin is added. At the fuller 20 litres per person per day UNHCR plans against, it is 200,000 litres (200 m³).
What is the Sphere minimum for water quantity per person per day?
7.5 to 15 litres per person per day for basic survival, drinking, cooking and hygiene, with a water point within 500 metres of the furthest dwelling and a queue time no longer than 30 minutes.
Why do several smaller tanks work better than one large tank of the same total volume?
Because a single tank is a single point of failure: one liner fault or one cleaning cycle takes out all of it. Several tanks, for example four Oxfam T95 units of 95 m³ each, can be sited nearer separate tapstand clusters, staged in as trucks allow, and kept running individually while one is serviced.
How much reserve should be added to straight daily demand?
There is no single Sphere figure for it. Reserve is an engineering judgement against your own delivery reliability, sized to cover the specific interruption being protected against, a missed trucking run, a borehole outage, or population growth ahead of the next planning cycle, and it should be stated as an explicit assumption in the design rather than left implicit.
When should camp water storage be re-sized?
Whenever the planning population changes materially, not on a fixed schedule. Sudden displacement and outbreak response both move a site's caseload faster than routine counts capture; South Sudan's 71,825 suspected cholera cases between January and mid-August 2025 is one example of how fast a caseload can move. Re-run the same population-times-target-plus-reserve calculation against the new figure.
Related reading
Specialized Logistics Solutions is an in-country distributor headquartered in Juba, an authorised distributor for Aquatabs (Medentech/Kersia), P&G Purifier of Water, Oxfam tanks and bladders (Butyl Products UK), Multiquip and Aussie Pumps, and a UNGM-registered vendor (No. 380716). Our authorised Oxfam tank range covers the T11 through T95 sizes referenced above, held in-country and supplied to UN agencies and NGOs across South Sudan, Uganda and DR Congo. Request a quotation from SLS and we will help you run the population-to-tank-configuration maths for your own site.
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