Fast access to stored water. A compact tank to transport when empty. Open-top systems for firefighting water staging, irrigation, construction washdown and temporary field operations.
DERFLEX supports project-specific self-supporting onion tanks and frame-supported flexible tanks using reinforced PVC coated fabric, with TPU material alternatives reviewed where appropriate. Capacity, operating depth, inlet/outlet details, foldability and packing are matched to your application—not assumed from a generic catalogue size.
An open-top flexible water tank stores water in a reinforced, waterproof coated-fabric structure with no fixed closed roof. Depending on its design, the wall is supported by the contained water and a shaped rim, or by a separate structural frame.
Open access makes these tanks useful when operators must fill rapidly, dip a suction line, observe the water level, wash equipment or draw water repeatedly. The same open surface also introduces splash, evaporation, debris and hygiene considerations that a closed bladder avoids.
For the wider family of closed and open containment systems, explore DERFLEX heavy-duty tarpaulin tank solutions.
An onion tank, a framed open tank and a closed bladder may all be portable—but they solve different operational problems. Start with how the water will be accessed, and how the perimeter will stay stable.
Usually formed from a tapered or specially shaped flexible body with a supporting rim. The wall geometry stabilizes as the tank fills. Useful where fast deployment and direct access are priorities.
A coated-fabric liner is carried by a project-matched tubular or engineered frame. The perimeter remains more defined and can be useful for repeated access and site integration.
For longer storage, mobile enclosed water supply or contamination-sensitive projects, a closed flexible tank can be preferable to an open water surface.
Open-top systems should be specified as complete assemblies: fabric, geometry, rim or frame, seams, drains and site interface. The values below are specification fields, not unverified stock-model promises.
| Specification | DERFLEX project direction | What your drawing / RFQ should confirm |
|---|---|---|
| Tank format | Self-supporting onion / open-top framed liner | How the wall and rim are supported throughout filling and emptying |
| Usable capacity | Custom to agreed geometry and safe operating level | Required liters or m³, freeboard, maximum water depth and footprint |
| Material | Reinforced PVC coated fabric; selected TPU coated fabric subject to review | Stored water quality, coating, base textile, UV exposure, folding duty |
| Fabric thickness / weight | Project-specific; existing DERFLEX flexible tank references include selected 0.75–1.20 mm constructions, not universal open-top specifications | Approved material datasheet, tensile, tear and welding requirements |
| Seams & reinforcement | Fabric-compatible welded seams and local stress reinforcement | Joint design, patch size, attachment points and inspection criteria |
| Top rim / frame | Designed according to tank type; structural details by project | Frame material, connection arrangement, edge attachment, safe support |
| Drain system | Custom drain and hose interface options for review | Drain point, fitting size, thread / coupling type, valve, flow target |
| Accessories | Groundsheet, cover, repair components, packing options by request | Cleanability, intended weather exposure, transport and deployment cycle |
| OEM supply | Color, logo, labels and export packing can be discussed | Approved drawings, model codes, order volume, destination and QA scope |
Specification caution: the published broad DERFLEX flexible-tank family is not a guarantee that every volume or thickness is suitable for an unsupported open-top design. Final working capacity and construction require project confirmation.
Nominal capacity claims are easy to misunderstand in flexible containment. An open rim must maintain suitable freeboard above the operating waterline to reduce spill risk during hose movement, pumping, wind or nearby activity. Shape changes under load also affect volume.
For a theoretical 2.0 m × 2.0 m basin with 0.6 m working water depth: 2 × 2 × 0.6 × 1,000 = 2,400 L. This is a geometric example only—not a DERFLEX rated tank capacity. Real capacity must account for wall profile, frame/liner geometry, freeboard and operating limits.
For larger engineered storage projects, see the separate large-capacity flexible water tank guide. High volume does not automatically mean that an open-top format is the most suitable choice.
Volume available within the project-approved operating fill level.
Controls hydrostatic load, access height and practical draw-off.
Reserve height above the waterline, assessed for actual operating conditions.
Includes the frame, tank perimeter, hose access and safe clearance.
Tank material must resist hydrostatic load, abrasion, folding stresses and outdoor exposure while forming sound seams and reinforced fitting interfaces. Material selection should follow the stored liquid, operating temperature, use cycle and destination requirements.
PVC coated polyester is a practical starting point for many industrial, agricultural and temporary water-storage applications. TPU coated fabric can be evaluated for selected flexibility, abrasion or folding requirements; suitability is grade- and design-dependent.
Where water is intended for drinking, neither the words “PVC” nor “TPU” demonstrate potable-water approval. The exact contact surface, fittings and assembled system must meet the relevant documented market requirements. Review potable-water liner material considerations before requesting such a product.
Testing and certification are specified by project; no universal approval or test result is asserted for every tank configuration.
An open top solves accessibility but does not replace engineered connections. Operators need controlled filling, a predictable draw-off method and a way to drain residual water without stressing the liner.
Define hose diameter, target filling rate and how incoming flow is directed. Avoid concentrated jets hitting unsupported fabric or the tank base.
Provide room for suction lines, inspection, cleaning or repeated water pickup. Plan splash and debris control around an exposed water surface.
For self-supporting tanks, confirm the water level required to maintain shape. For framed tanks, inspect liner support and manage hose loading.
Plan an accessible drain path, safe residual-water removal, drying and folding. Do not lift, drag or relocate a filled tank.
The reason to select an open tank is usually the work happening around its water surface. The correct material and support method still depend on the site and use cycle.
Temporary reservoir for filling, suction or water relay at remote operations. Confirm coupling and pump arrangement, required flow and local fire-service expectations.
Accessible temporary water for surface cleaning, equipment washing and jobsite utility support. Review containment of dirty water and local discharge rules.
Open intermediate water holding for irrigation filling points, mobile farm operations and seasonal distribution. Consider algae, debris and evaporation management.
Framed flexible pools can support temporary fish holding, cleaning or maintenance operations where species needs, oxygenation and water quality are addressed separately.
Compact-to-transport open reserve for temporary operations. A protected closed water-storage solution is preferable when hygiene and prolonged storage dominate.
Selected temporary non-potable water holding. Check exact liquid chemistry, wastewater controls, leak consequences and whether secondary containment is required.
Actual DERFLEX site photography pairs coated-textile surface detail with a frame-supported aquaculture tank, linking material selection to the assembled system.
Compare coating finish, surface texture and liner flexibility. Material imagery is illustrative; the approved grade and test data must match the water-storage design.
A more defined operating shape, accessible water surface and visible drain connection. Species management and water quality remain separate design issues.
For procurement, compare the operating system rather than assuming all open-top tanks are interchangeable.
| Decision variable | Self-supporting onion tank | Frame-supported tank |
|---|---|---|
| Set-up | Typically minimal rigid assembly; shape depends on design and water level | Frame assembly or fold-out operation required, depending on model |
| Perimeter shape | Flexible and may change with fill level | Defined by the supported rim / frame |
| Working at low fill | Requires specific stability assessment | Wall perimeter generally supported by frame; liner still requires correct installation |
| Transport | Flexible tank packs down without a large rigid wall structure | Includes frame components; folded size and weight must be quoted |
| Maintenance | Inspect rim and flexible support geometry | Inspect liner attachment, frame joints and wear points |
| Best reason to choose | Fast field deployment and minimal structural handling | Regular access and a more predictable installed footprint |
Actual properties are construction-specific. Ask for the approved product drawing and installation instructions before comparing models.
A flexible liner is only as protected as the surface beneath it. Ground defects, settlement and misrouted hoses can create localized load or abrasion even when the coated fabric itself has suitable strength.
For slopes, retaining structures, large stored volumes or public-access locations, use a site-specific engineering and safety assessment. Do not rely on generic slope or wind-load claims.
The tank may not fit the installation area.
Freeboard and operating limits are overlooked.
A self-supporting shape may change during draw-down.
Tank operations become slow or create fitting loads.
Required contact approvals and hygiene are missing.
DERFLEX works across reinforced coated fabrics and fabricated water-containment products. That makes it possible to discuss tank material, seams, reinforcement, geometry, fittings and OEM presentation as one procurement brief rather than unrelated components.
For a new size or recurring supply program, ask for a defined approval route: confirm application inputs, select structure, approve material and fitting details, review drawing/sample requirements, agree inspection points and freeze packing details for repeat orders.
Custom tank model development and DERFLEX custom tarpaulin tank engineering are reviewed against the full project requirement.
A project inquiry should allow the engineering and sales teams to understand the filled condition, operating waterline, usage cycle and connection system—rather than just quoting a price per liter.
For distributors building a multi-model range, review bulk water tank and private-label sourcing alongside your product specification.
Send Your Tank Requirements ↗MOQ, unit price, confirmed lead time and test documentation depend on the approved construction and production order; request these on the formal quotation.
Straight answers to the questions that most often change a project specification.
It is a portable water-holding tank made from reinforced waterproof coated fabric, with an accessible upper opening. It may be self-supporting with a floating or shaped rim, or supported by a folding or assembled frame.
An onion tank develops its operating shape through its flexible wall geometry and water fill, generally without a rigid external frame. A frame-supported tank uses a structural frame to hold its liner and maintain a more predictable perimeter.
Specify usable water capacity, available footprint and maximum operating water depth. Allow for freeboard, the real tank shape and water movement; do not calculate usable capacity from outside rim dimensions alone.
Do not assume an open-top flexible tank is suitable for potable water. Drinking-water projects require suitable certified wetted materials and fittings for the destination market, plus a hygienic system design and contamination controls.
They can be considered for temporary fire-water staging where rapid water access is needed, subject to compatibility with pumps, hose couplings, draw-off rate, site layout and local operating requirements.
DERFLEX can review custom capacity, footprint, PVC or TPU coated fabric, reinforcement, outlets, drain valves, colors and OEM packaging against the project drawing and intended operating conditions.
Drain using an approved method, remove sediment, clean using a method compatible with the coating and stored liquid, rinse as required, fully dry before folding, and store away from sharp objects and damaging environmental exposure.
Tell DERFLEX your required working liters, footprint, tank support preference, water type and hose arrangement. We can review an appropriate coated-fabric construction and quotation scope for your project or OEM range.
For custom engineering, include a sketch or site drawing wherever possible. No unconnected form on this page.