Convert usable water volume into a completed-vehicle load
For preliminary work, one cubic metre of water is commonly close to one tonne. State the density and temperature basis rather than treating that approximation as the final calculation. Filling and water-service requirements can reduce the usable volume below the shell’s nominal capacity.
Add the finished tank, subframe, pump, equipment and operating items to the load review. Check the actual tank layout and full and partial-fill conditions. Baffles, geometry and grade affect liquid position, so a centered point-mass assumption cannot stand in for the approved axle calculation.
Reconcile usable fill with gross and axle limits
If the requested water volume does not fit within the completed vehicle’s limits, change the fill allowance, layout or chassis. The fact that the shell can physically hold the volume is not permission to carry it.
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| Decision | What to establish | Condition or limit |
|---|---|---|
| Water mass | Multiply usable volume by the approved density basis. | Liters are volume, not payload mass. |
| Completed tare | Include tank, subframe, equipment and every installed option. | Bare chassis curb mass cannot be subtracted directly from gross mass. |
| Axle reactions | Calculate each relevant loaded and partial-fill condition. | Passing gross mass does not prove axle compliance. |
| Usable fill | Apply venting, operating and water-service allowances. | Geometric shell volume is not automatically usable delivery volume. |
Turn nominal water volume into a payload check
Convert the water volume to mass, then add the vehicle and operating items. Check that total against the gross limit and verify the load on each axle.
The illustrative loaded mass is 25,200 kg. Nominal tank volume is acceptable only if the selected chassis, completed tare and load distribution remain within every controlling limit.
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| Step | Calculation or condition | Result |
|---|---|---|
| Liquid mass | 12 m³ × 1,000 kg/m³ | 12,000 kg |
| Loaded mass | 13,200 + 12,000 | 25,200 kg |
| Approval gate | Loaded mass and each axle reaction ≤ approved limits | Both must pass |
- Nominal water volume: 12 m³
- Illustrative water density: 1,000 kg/m³
- Completed vehicle, crew and equipment mass: 13,200 kg
Illustrative density and masses only. Use the actual liquid specification, weighed tare, controlled tank drawing and selected chassis limits.
Choose delivery capacity around the refill cycle
Start with the receiving site: what is the water for, how much must arrive, and when can it accept delivery? Separate drinking-water service from construction or other non-potable supply before selecting the tank and transfer equipment. Then test whether the legally permitted delivery volume and realistic trip count can meet that demand.
WHO's tanker-planning example includes filling, travel, unloading and return travel before calculating fleet requirements. Apply that sequence using your own measured times. Its emergency-supply example is not a productivity promise for your route. WHO: Delivering safe water by tanker
Demand and acceptance
Record the water use, receiving storage, delivery window and volume accepted per visit. Confirm any water-quality and dedicated-service requirements.
Refill availability
Record source opening hours, queue time, loading connection and observed filling time. Include an alternative plan if the source cannot supply the planned trips.
Vehicle and schedule
Use the approved usable fill after gross and axle checks. Add the complete round trip and handling time, then compare achievable deliveries with the site demand; revise the schedule or fleet if it falls short.
Ask for the permitted delivery volume and its calculation basis
Provide the water service, density basis and intended fill conditions. Request the completed tare and axle review, including venting and operating allowances. Then use that permitted volume with realistic trip times to assess the delivery requirement.
Information to prepare for this review
- Requested usable water volume
- Controlled water-density assumption
- Completed tank-system mass
- Chassis curb, gross and axle ratings
- Crew, fuel, hoses, tools and options
- Tank position, compartments and credible fill cases
Records to request and keep
- Controlled tank-volume definition
- Water-density and operating allowance basis
- Completed tare and equipment schedule
- Gross and axle-load calculation for approved load cases
Common mistakes and what to check instead
- Treating 10,000 L as a 10,000 kg payload line without context: State density, usable fill and all completed-vehicle masses.
- Using chassis curb weight as finished tare: Add tank, subframe, pump, hoses, crew, fluids and options.
- Checking only full load: Review credible partial-fill and axle-reaction cases required by the design.
Scope of this guide
This guide provides a preliminary calculation structure, not an engineering approval.
The selected chassis, tank design and destination mass rules control final capacity.
Reject or pause the configuration if tare, density, usable fill, axle reactions or legal limits are not controlled.
Sources and applicability
Emergency drinking-water planning reference for delivery cycles and fleet requirements, not a universal application rate or vehicle approval.
Pages 1–2, logistics and Box 12.1
Document date:
Sources checked:
Controls the project-input, quotation, approval and inspection workflow described in this guide.
Provides public checklists and worksheets; the signed project documents remain controlling.
Defines the relevant product family and published configuration boundaries. Project-specific ratings require the selected OEM documents.
Manufacturer example supporting tank, pump, PTO, valve and leak checks. Its component limits are model specific and not KEEYAK ratings.