Getting the size right is the most important decision when you plan water storage in the UAE. A tank that is too small leaves you short during peak demand or a supply interruption. A tank that is too large costs more to build, takes up valuable space and can hold water for so long that it turns stale and warm. This guide shows you how to calculate water tank size in the UAE step by step, with realistic per-person figures, worked examples for a villa, a labour camp and an apartment building, and a quick litres-to-gallons reference.
The Basic Water Tank Sizing Formula
Every water tank capacity calculation starts with the same simple idea:
Each part of the formula matters:
- Number of users: residents, workers, students, guests or rooms. Use the design occupancy if the building will fill up over time, not just today's numbers.
- Daily demand: the litres each user consumes per day. This varies widely by building type (see the table below).
- Days of storage: how long the tank must supply water without refilling. One day is common where mains supply is reliable. Two or more days makes sense when supply is intermittent or you depend on tanker deliveries.
- Safety margin: an extra 10–20% to cover peak days and future growth.
Fire-fighting water is not part of this number. A fire reserve is calculated separately and held in a dedicated tank or compartment. Our guide to fire water storage tanks in the UAE explains how that works.
Typical Daily Water Demand by Building Type
The figures below are indicative planning ranges often used at concept stage. Your MEP consultant and local water authority (such as DEWA in Dubai or SEWA in Sharjah) set the final design values, so treat these as a starting point rather than a code requirement.
| Building type | Unit | Indicative demand (litres per day) |
|---|---|---|
| Villa or apartment | Per person | 200 – 300 |
| Labour camp or staff accommodation | Per person | 100 – 150 |
| Office building | Per person | 40 – 70 |
| School | Per student | 45 – 70 |
| Hotel | Per room | 400 – 800 |
| Factory or warehouse (sanitary use) | Per worker | 45 – 60 |
Process water, cooling make-up, landscaping and irrigation come on top of these figures and depend on the operation, so calculate them separately.
Worked Examples
Example 1: Villa with 8 residents
8 people × 250 L = 2,000 L per day. Two days of storage gives 4,000 L, and a 20% margin brings the requirement to about 4,800 L. A standard 5,000-litre tank (roughly 1,100 imperial gallons) is the right fit.
Example 2: Labour camp with 300 workers
300 workers × 135 L = 40,500 L per day. With one day of storage and a 20% margin you need about 48,600 L, so a 50,000-litre installation (around 11,000 imperial gallons) works. Consider two 25,000-litre tanks or a two-compartment tank so one side stays in service while the other is cleaned. The same logic applies to any industrial or labour camp water storage project.
Example 3: 120-apartment building
120 apartments × 4 residents × 225 L = 108,000 L per day. One day of storage is about 108 m³ before margin, usually split between a ground or underground tank and a roof tank. Your consultant sets the split based on pump capacity and building height.
Litres, Cubic Metres and Gallons: Quick Conversions
Quotes in the UAE are often given in imperial gallons, while drawings use cubic metres, so it helps to convert quickly. Remember that 1 m³ = 1,000 litres, 1 imperial gallon = 4.546 litres and 1 US gallon = 3.785 litres.
| Litres | Imperial gallons (approx.) | Cubic metres |
|---|---|---|
| 5,000 | 1,100 | 5 m³ |
| 10,000 | 2,200 | 10 m³ |
| 20,000 | 4,400 | 20 m³ |
| 50,000 | 11,000 | 50 m³ |
| 100,000 | 22,000 | 100 m³ |
For the geometry, capacity in cubic metres = length × width × usable water depth. Usable depth is slightly lower than wall height because the water level sits below the overflow, so always confirm the working capacity and not just the nominal figure.
Rooftop vs Ground Tanks: How Placement Limits Capacity
One litre of water weighs one kilogram, so a 5,000-litre roof tank adds around five tonnes before you count the tank itself. Roof structures have load limits, which is why rooftop tanks are usually smaller and most of a building's storage sits at ground level or underground and is pumped up. Always ask a structural engineer to confirm what your roof can carry before you fix a rooftop tank size.
Factors That Change Your Tank Size
- Supply reliability: if mains supply is unreliable or you rely on tankers, add storage days.
- Peak demand: hotels, camps and schools have sharp morning and evening peaks that stress an undersized tank.
- Cleaning access: tanks need regular cleaning, so splitting capacity keeps water flowing while one side is out of service. See our water tank cleaning and disinfection guide for the schedule.
- Location: rooftop, ground-level and below-grade tanks have different space and load limits. Our underground water tanks guide covers the below-grade case.
- Future expansion: sectional pre-engineered tanks make phased capacity easier to plan than a poured structure.
- Budget: cost rises with capacity, though not in a straight line. Our water tank price guide explains what drives it.
Common Sizing Mistakes to Avoid
- Sizing for average demand instead of peak demand.
- Forgetting the fire reserve, or mixing it into domestic capacity without approval.
- Installing one large tank with no way to isolate it for cleaning or repair.
- Ignoring foundation size, site access and maintenance clearance.
- Oversizing. Water stored too long in a hot climate loses its disinfectant residual and warms up, as we explain in our guide to keeping stored water cool in the UAE summer.
Choosing the Right Tank Once You Know the Size
With a capacity in hand, the next step is material and system. Zincalume and GI steel panel tanks suit large volumes and fast erection, while GRP panel tanks suit rooftops and corrosive locations. Compare them in our steel vs GRP vs concrete vs HDPE water tank comparison, read the GI vs Zincalume breakdown and browse the complete guide to water storage tanks in the UAE to shortlist options.
Frequently Asked Questions
How many litres of water tank does a villa need?
Many villas are well served by 3,000 to 10,000 litres, depending on the number of residents, garden use and the days of storage you want. A family of six using about 250 litres each per day needs roughly 1,500 litres daily, so a 3,000-litre tank gives about two days of storage.
How do I convert litres to gallons?
Divide litres by 4.546 for imperial gallons or by 3.785 for US gallons. For example, 10,000 litres is about 2,200 imperial gallons.
Should I install one large tank or two smaller ones?
For commercial projects, two tanks or a two-compartment tank is usually better because one side can be isolated for cleaning or repair while the other keeps supplying water.
Does the tank size include the fire-water requirement?
No. Fire-water storage is calculated separately according to the fire protection design and local authority requirements, and is normally held in its own tank or a dedicated reserve compartment.