Fewer assembly steps
Eliminating a separate rigid support frame reduces components to move and assemble. Ground preparation and controlled filling remain essential.
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Field-deployable water storage / OEM supply
Self-Supporting Water Tanks
Frameless, collapsible onion tanks for rapid-access water reserves. Built around the realities of field deployment: available footprint, self-rising collar geometry, coated-fabric integrity, fill-and-drain connections, and repeatable OEM specifications.
No rigid external frameSelf-rising sidewalls during filling. Final geometry depends on the engineered tank design.
Open-top field accessSimple filling and water-level observation
Self-rising collarFloating rim follows the water level
Compact after emptyingFlexible fabrication for field logistics
Application-led sourcingFittings, water type and site reviewed together
The essential distinction
Think “onion tank,” not “water pillow.”
Both are collapsible systems. Their operating geometry, exposure to contamination and access requirements are different.
What Is a Self-Supporting Water Tank?
A self-supporting water tank is a frameless, flexible water reservoir, commonly called an onion tank, pumpkin tank or self-rising water tank. Reinforced coated-fabric walls and a buoyant top collar rise as the tank fills, forming an open, accessible reservoir without a rigid external support frame.
It is particularly useful when field crews need quick access to stored non-potable water without erecting a steel or tubular frame. Empty, the tank folds for transport; full, it must remain on a prepared, load-bearing surface and within the approved usable fill level. A cover may reduce debris entry but does not by itself create a certified potable-water system.
Open accessTop-fill and visual inspection
CollapsibleReduced empty-state transport volume
Project-specificCapacity, profile, material and fittings
How the structure actually works
Self-Rising Geometry, Not a Hidden Metal Frame
The distinguishing component is a buoyant rim or collar integrated around the opening. As water is introduced, the collar follows the water surface, helping the sidewall rise. Tank geometry, reinforcement and fill limit must work together to prevent excessive deformation or loss of freeboard.
- Collar design: confirm floating collar type, protective sleeve, handling details and any optional air-collar arrangement.
- Wall and base: size material strength, panel pattern, weld paths and abrasion protection for the filled shape.
- Overflow / fill control: establish an approved usable level, freeboard and a filling supervision procedure.
- Access vs security: open top enables rapid access but needs debris, animal, fall and contamination controls.
Built around real field workflows
Why Procurement Teams Specify Frameless Onion Tanks
The benefit is not only that a tank folds. It is that temporary water capacity can be moved, deployed, used and recovered as a complete field system.
Quick open-top operation
Allows direct hose filling, visual water-level checks and project-specific drafting or pumping arrangements.
Compact when drained
Folded coated fabric occupies less empty-return space than a rigid reservoir of comparable installed capacity.
Material and weld matching
Reinforcement, coating adhesion, seam overlap, edge construction and valve reinforcement can be evaluated as a system.
OEM configuration control
Discuss color, product marking, packing, spare accessories, fitting layout and repeat-order technical documentation.
Application-first options
Match tank type to stored liquid, pumping requirements, contamination risk, exposure and the available site footprint.
Technical sourcing framework
Self-Supporting Water Tank Specifications
Use the parameters below to prepare an RFQ. They are material and design directions, not a universal performance datasheet for every onion tank size.
| Specification | DERFLEX project direction | What the buyer should confirm |
|---|---|---|
| Tank architecture | Frameless, open-top onion / self-rising geometry; covered concepts can be discussed. | High- or low-side profile, permitted filling method and required access. |
| Capacity | Custom capacity subject to approved onion tank geometry and engineering review. | Nominal versus usable volume; do not assume the full flexible-tank family range applies to an onion design. |
| Liquid-contact material | Reinforced PVC coated polyester; TPU coated textile can be evaluated where appropriate. | Water type, liquid temperature, storage duration and relevant compliance. |
| Coated-fabric thickness | DERFLEX flexible-tank material references include approximately 0.75–1.20 mm; final onion tank specification requires confirmation. | Approved fabric construction, reinforcement, thickness, strength and welding behavior. |
| Reinforcement | Polyester woven substrate; 1000D-class constructions exist in DERFLEX water-containment material references. | Warp/weft strength, tear resistance, load paths, coating adhesion. |
| Collar / top rim | Buoyant self-rising collar design and optional project-specific rim details. | Collar section, joining, handling points, maintenance and fill-limit markings. |
| Panels and seams | HF / RF or other compatible thermal welding, selected by material and tank geometry. | Sample weld validation, seam map, panel layout and fitting reinforcement. |
| Connections | Outlet, drain, flange, threaded or quick-coupling options according to drawing. | Hose size, thread/flange standard, pump flow, outlet location and support. |
| Accessories | Optional cover, groundsheet, marking, carrying/packing bag and repair-kit discussion. | Accessory compatibility, contents and packing specification. |
| Environment & compliance | Outdoor formulation and contact requirements assessed for each order. | UV exposure, site temperature, potable-water restrictions and destination standards. |
Technical accuracy: existing DERFLEX product references describe several flexible tank constructions, not one certified self-supporting tank series. Exact onion-tank capacity, base diameter, top diameter, filled height, weight, temperature limits, fittings, certificates and lead time must be confirmed in the project drawing and quotation.
Material choice
PVC or TPU? Start With the Water and Duty Cycle
Coating chemistry alone does not prove tank performance. The substrate, double-side construction, weld compatibility and intended liquid must be reviewed together.
Widely used containment direction
PVC-Coated Polyester
A practical construction for many general-service, non-potable outdoor reservoirs where reinforced fabric, weldability and commercial cost are key purchasing considerations.
- Reinforced textile load-bearing layer
- Waterproof PVC coating and weldable surfaces
- Can be tailored for exposure and abrasion needs
- Sample weld and finished-tank leak evaluation recommended
Specialized project direction
TPU-Coated Technical Fabric
Worth evaluating when repeated folding, flexibility or a particular water-contact formulation is a priority. Material selection must not be equated with automatic food- or drinking-water approval.
- Polyester or nylon reinforcing base options
- Grade-dependent flexibility and weld processes
- Polyether TPU may be considered for hydrolysis resistance
- Project-specific contact and finished-system testing
If the stored medium is fertilizer solution, industrial liquid, wastewater or anything other than ordinary water, provide the exact composition and exposure conditions before seeking material approval. Fuel and aggressive chemicals are not automatically compatible with this product.
Visual product references
Actual DERFLEX Water-Containment Images
The hero image above shows DERFLEX’s self-supporting onion shape. The following different images illustrate related tank structures and a coated-fabric detail for comparison; they are not presented as onion-tank models.
Decision matrix
Self-Supporting vs Pillow vs Frame-Supported Tanks
The right tank format is determined first by access, water quality controls and site conditions, not by a preferred marketing name.
| Buyer requirement | Self-supporting onion | Closed pillow / bladder | Frame-supported liner |
|---|---|---|---|
| Open top access | Yes; key advantage | No; sealed/port access | Yes |
| Rigid assembly frame | Not required for designed self-rising configuration | Not required for typical ground-supported bladder | Required |
| Contamination protection | Requires cover and a hygiene plan; open reservoir limitations remain | Enclosed configuration is generally preferable | Requires cover and site controls |
| Installation geometry | Flexible footprint and side height vary with fill | Low-profile expansion as filled | Frame defines supported shape |
| Typical procurement priority | Field reserve, fast access, temporary firefighting water | Enclosed temporary storage and compact logistics | Stable open working tank and repeated access |
Where access and deployment matter
Applications of Self-Standing Water Tanks
Each setting has a different balance of water quality, site loading, hydraulic connection and turnaround requirements.
Firefighting Water Reserve
Temporary water supply at rural or remote staging areas. Confirm pump coupling, usable volume, safe access and local emergency-service requirements; not every configuration is suitable for aerial dipping.
Agriculture & Irrigation
Seasonal reserve for irrigation crews and farms. Evaluate turbidity, debris, hose connections, weather exposure and storage period.
Construction Sites
Short-term process or dust-control water where access, site footprint and ground protection are planned in advance.
Emergency Response
Rapidly deployable non-potable water reserves at field camps, relief sites or temporary works. Hygiene and user access controls are project-specific.
Industrial Field Services
Temporary clean-up or service-water buffer systems where the liquid is verified as compatible and discharge is controlled.
Distributor & OEM Programs
Repeated product ranges with specified colors, markings, connection standards, accessory kits and export packing.
Capacity, usable volume and site reality
Specify the Filled Footprint—Not Just the Liters
A 10,000 L water reserve holds approximately 10 metric tonnes of water, before adding fabric or equipment weight. A flexible tank also changes profile during filling. That is why a capacity-only quotation is not enough.
Ask for a project drawing showing base diameter, top opening diameter, expected filled height, maximum usable water level, discharge point and packed dimensions. Confirm that the substrate can accommodate the resulting filled footprint and total load. Never estimate dimensions from a simple cylinder formula when the tank has a curved onion profile.
Site planning principle: 1,000 L of water corresponds to about 1 m³ and approximately 1,000 kg of water mass. This is a mass relationship, not a site-bearing-capacity approval.
Design review sequence
01 Target usable volume
→
02 Site diameter / footprint
→
03 Water access & operating level
→
04 Collar + sidewall geometry
→
05 Fabric / seams / fittings
→
06 Packing and inspection plan
✓
Field use matters as much as fabrication
Deployment and Handling: Six Points to Get Right
Use the approved product manual and local site procedures. These principles help procurement teams decide what instructions, accessories and risk controls to ask for.
- Assess the groundChoose a stable, adequately load-bearing area; verify slope limits with the tank manufacturer and remove debris and sharp objects.
- Protect the bottom surfaceUse an appropriate clean groundsheet or underlay where abrasion and puncture could occur.
- Lay out the collar and wallOpen the tank carefully, inspect the fabric and seams, and ensure the rim is unobstructed before filling.
- Control fillingFill under supervision; allow the buoyant rim and walls to rise evenly and stop at the approved operating level.
- Manage hoses and accessSupport heavy hoses, keep suction s, ystems and equipment from damaging fabric, and control access around the open water.
- Drain, dry and packFollow site procedures, clean and dry appropriately, inspect collar and welds, and avoid sharp folds or contaminated long-term storage.
Not recommended: moving a tank while filled, towing it by fittings, overfilling, placing it on unverified sloping ground or using an unapproved open-top tank for drinking-water storage.
Manufacturing & quality review
The Controls Behind a Reliable Field Tank
DERFLEX supplies reinforced coated fabrics and finished flexible tank directions. For a self-supporting tank, the buyer should ask to review the complete fabric–collar–seam–fitting system before repeat orders.
Reinforcement & coating
Confirm weight, thickness, strength directions, coating adhesion and weather suitability on the chosen construction.
Rim construction
Review buoyancy, sleeve seams, joining and the relationship between collar geometry and the approved water level.
Panel strength
Use compatible joining methods with meaningful seam and fitting sample checks; do not approve by fabric GSM alone.
Stress reinforcement
Check outlets, flanges and hose interface layout where concentrated loads and pump forces may occur.
Workmanship & fill test
Define visual checks, dimensional inspection and project-appropriate leak or water-holding acceptance criteria.
Repeatable specification
Document approved color, collar, fabric, seam map, fittings, accessory kit, markings and packing for future orders.
For project managers, distributors & OEM buyers
A Better Tank Quotation Starts With Eight Details
Send your intended operating conditions, not only a requested price per liter. DERFLEX can discuss an appropriate tank construction and suitable material direction for your project.
For repeat-order programs, request a drawing and technical confirmation before approving bulk fabrication. A quotation does not replace site engineering or a required potable-water / fire-service compliance review.
- 01 · WaterExact stored water / liquid and required documentation
- 02 · CapacityNominal and required usable volume
- 03 · DimensionsAvailable ground area and height / access limit
- 04 · Water handlingFilling, pump-out and coupling requirements
- 05 · SiteSurface, slope, UV and ambient temperature
- 06 · LifecycleFrequency of folding, relocation and maintenance
- 07 · OEMMaterial, color, logo, cover, groundsheet, packing
- 08 · CommerceQuantity, destination, samples and target schedule
Continue your engineering review
Related DERFLEX Water Storage & Materials
Explore the other tank architectures and coated-fabric material routes before locking your project specification.
Heavy Duty Tarpaulin TanksCompare full flexible containment architectures and construction priorities.
Collapsible Water Storage TanksReview packing, field logistics and empty-state storage planning.
Flexible Water BladdersEvaluate closed pillow-style tanks when open-top access is unnecessary.
TPU Flexible Tank FabricConsider alternative water-contact and foldable material constructions.
PVC-Coated Polyester FabricExplore coated textile reinforcement, surface and fabrication choices.
Industrial Flexible Liquid TanksReview liquid compatibility, containment layouts and industrial use.
Frequently asked by buyers
Self-Supporting Water Tank FAQ
Clear technical answers before purchasing and deployment.
What is a self-supporting water tank?
A self-supporting water tank is a collapsible, frameless flexible tank whose sidewall and buoyant collar rise as water is introduced. Also called an onion or pumpkin tank, it is typically an open-top reservoir for temporary field storage.
Does a self-supporting onion tank need a metal frame?
No rigid metal frame is needed for a properly designed self-supporting onion tank. The coated-fabric wall, buoyant collar, geometry and contained water work together. It still needs a suitable prepared site and operation within the approved water level and ground limits.
How is an onion tank different from a pillow water bladder?
An onion tank is normally an open-top, self-rising tank with direct field access. A pillow water bladder is enclosed and expands into a low-profile shape during filling. Choose the onion style for rapid open access; choose a closed bladder when enclosed storage is a priority.
Can self-supporting water tanks be used for firefighting?
Yes, the design is used for temporary fire-water staging and field reserve systems. However, the selected tank must meet the project’s required capacity, access height, pump suction or outlet dimensions, safe deployment conditions and applicable local fire-service specifications. Never assume every tank supports helicopter dipping.
What material is suitable for a self-standing water tank?
Reinforced PVC coated polyester is a common material for weldable outdoor flexible tanks. TPU coated fabric can also be evaluated for specific projects. Suitability depends on filled height, tensile and tear properties, seam quality, folding cycles, water type, climate and any required testing.
Are self-supporting water tanks suitable for drinking water?
Do not assume ordinary open-top PVC or TPU field tanks are approved for drinking water. Potable use needs suitable hygienic containment, water-contact materials, valves and finished-system documentation for the destination market. An open-top cover alone is not proof of potability.
What details should I provide for a custom water tank quotation?
Provide target usable capacity, available footprint, water type, operating temperatures, pumping and filling method, connection requirements, preferred material, deployment frequency, quantity, destination and required tests or certifications. If possible, attach a site or product drawing.