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Water Storage Tanks – One Piece

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One Piece Storage Tanks

Structural strength is provided by polyester resin and glass fibre

One Piece Water Storage Tank

reinforcement, which is finished internally with a smooth impervious isophthalic gel coat.

The gel coat finish on both the tank and lid ensures that harmful bacteria are not offered a surface on which to grow. Furthermore, all IWE gel coats and colouring pigments are lead-free. To ensure water quality, the resin and gel coats are pigmented throughout to prevent the ingress of light. (Light entering a tank permits the organisms that are already present to multiply, which would contaminate the supply.)

In order to prevent osmosis (a condition whereby water is absorbed into the laminate), it is necessary to implement strict manufacturing controls during the production of water tanks and cisterns. At IWE, we have implemented key elements into our manufacturing process in order to prevent osmosis. We ensure that the required amount of catalyst needed to cross-link and cure the polyester resin is measured precisely. We also ensure that a constant temperature is maintained throughout our manufacturing facility, as temperature is an essential factor in the correct curing of laminates.

IWE tanks are given a full water test and results are recorded, ensuring that quality is followed throughout the design, production and finishing processes. Within the procedures documented in the IWE EN ISO 9001 quality manual, full records are retained and each tank is clearly identified for traceability. Core materials, when used, are compatible with the laminate and are completely encapsulated within the structure.

Base Support

All tanks must be fully supported over the whole base area, with a support system designed to accept the tank and lid, together with the weight of contents and pipe work. Please note: clients are responsible for base support.

Marine ply bases can be supplied bonded into the laminate of a tank or as a separate loose item, cut to specific requirements. (G16.14)

Installation Access

IWE tanks are of rigid construction and care must be taken that the overall size will pass through all obstructions and fit into the space chosen for the installation. Please check before ordering.

When access restrictions prevent a one piece tank being used, any standard tank can be supplied divided into horizontal sections. Alternative solutions can also be considered.

One Piece Water Storage TankFittings

All tanks holding wholesome water must be fitted with a screened vent and screened warning/overflow pipe. Tanks holding over 1000 litres actual capacity will require a separate warning and overflow pipe, sized according to the incoming mains supply.

Options available:

  • 25mm thick insulation = 'U' value of 0.83 w/m²
  • 50mm thick insulation = 'U' value of 0.45 w/m²
  • 100mm thick insulation = 'U' value of 0.23 w/m²


All tanks are supplied with lids and each lid is fitted with a closed-cell approved gasket, adhesive on one side, enabling the air gap to be achieved. Stainless steel fixings secure lids in position.

Tanks holding in excess of 1000 litres actual capacity have lids which incorporate a bolted access for maintenance. Alternative opening mechanisms are also available to meet specific requirements.

Hot Water & Chemical Tank Options

Different resin systems are used for hot water and chemical storage. Feed and expansion tanks for the primary circuit are manufactured in hot water resins to ensure performance in the event of a thermostat failure. All one piece and split tanks are available in these options. A WRAS approved resin is available if required.

Division Plates

If there is a requirement to split the tank into two separate compartments, division plates are moulded into the tank, and the lid will therefore come in two pieces with a separate access in each piece.

Raised Valve Box "AA" or "AB" Air Gaps
To maximise capacity or to offer type "AA" or "AB" air gap a valve box may be included in the lid thus allowing either a valve with a drop arm or an Aylesbury KA/KB valve to be fitted.

When an "AB" air gap is needed we cut the required size slot in the side wall of the tank (dependant on inlet size). This is then covered with a specially moulded shroud which incorporates a screened mesh. Below this you can either use a drip tray or have a catchment tank fixed. Either of these options can be plumbed to discharge any overflow to a visible position. For type "AA" air gaps the screened mesh is omitted.

Weirs and Baffles

With the flexibility of our production techniques we are able to include weirs and baffle plates to meet customers' exact requirements.


IWE offers a full range of tank fittings. These can be purchased separately or as part of the package.