Every rainwater harvesting opportunity is different, so it makes sense that there is a range of tanks available, varying in size, shape and material. There is generally a model to suit most situations. Tanks can be manufactured from a range of materials; most are either (PE) polyethylene or GRP (glass reinforced plastic or ‘fibreglass’). Occasionally tanks are made from pre-cast concrete, though these are less common. Rainwater tanks can be either above ground or underground, or sometimes within a basement. Most above ground models are plastic, meaning they are easy to handle and relatively low cost.
Domestic Below-Ground Tanks
Underground tanks for garden or domestic use generally range from 1000 to 6000 litres, though sometimes bigger on larger properties. They tend to be either box-shaped or ‘submarine’ shaped; i.e. a horizontal cylinder with a vertical ‘turret’ on top. Some plastic box-shaped tanks are low-profile, which give the advantage of requiring only a shallow excavation. Generally known as ‘shallow-dig’ tanks these tend to be more expensive but obviously save on labour costs. Submarine tanks can be PE or GRP and are fitted with a turret which can usually be trimmed to suit finished ground level.
PE tanks are available in fixed sizes, as they are made from a mould. GRP tanks are manufactured in a different way so can more or less be made to any size, hence more choice is available. GRP tanks can also be structurally strengthened so are suitable for deeper excavations where required.
All underground rainwater tanks should be fitted with a calmed inlet which prevents turbulence as the water enters the tank. They should also be fitted with an anti-backflow device to comply with the British Standard; this ensures that no liquid can flow back into the tank e.g. from the storm drain (though where this is not possible, the backflow device can be incorporated into the overflow pipe run). The overflow should also ideally be ‘trapped’ (i.e. a U-bend as per a waste trap). Some models can also be fitted with rodent barriers if required.
Commercial Below-Ground Tanks
The majority of underground tanks for commercial projects are of GRP construction, because they can be manufactured to almost any size and are relatively easy to handle.
Commercial tanks can be anything up to around 100,000 litres; any larger than this and they become problematic to transport; — if a greater volume is required then two or more tanks can be linked together. Larger tanks can be fitted with access ladders if required, and can also have filter units built into them.
Other materials sometimes used for commercial tanks are reinforced plastic or pre-cast concrete.
Above-Ground Tanks For Garden Use
Above ground tanks come in a wide variety of styles and sizes, ranging from plain & simple barrels to elaborately decorative models that mimic architectural features or fun designs.
Most tend to be cylindrical in shape, or else ‘box’ shaped, which can be useful for siting against a wall or fence, or for where space is limited. Plainer models may not be particularly attractive, but can easily be screened or tucked away down the side of the house. They are simple to install, requiring only a firm level base.
Smaller gardens may only require a few hundred litres, a larger or more intensive garden might want several thousand. Large agricultural systems can also use above ground tanks, but on much larger scale – up to 30,000L for one-piece moulded tanks or even more when sectional tanks are used.
Above-Ground Tanks For Domestic Use
Most domestic rainwater harvesting installations use underground tanks, especially on new-build properties, but occasionally there is a need to have the tank above ground. For these situations upright PE tanks are commonly used; a wide range of sizes is available and they are easy to install, requiring only a solid level base on which to sit. The tank needs to be sited near to one of the rainwater downpipes, so for practical reasons it is usually only possible to connect one or two of these pipes to the tank. This will restrict the capacity of the tank due the limited amount of water that can be collected.
Special Above Ground Tanks
For some commercial projects, tanks are required to be sited in a basement or elsewhere within a building. If the capacity is very large or if the access is limited, such tanks are in sectional form, so are assembled on site by specialist contractors. Sectional tanks can also be used outside the building, permitting large storage volumes to be installed without the need to break ground.
To find out more about rainwater harvesting systems in general, please download our Ultimate Guide To Rainwater Harvesting Systems, a free e-book that explains the different types of rainwater collection system that can be used on domestic and commercial properties. Access a free copy by clicking here. For any other questions, please don’t hesitate to get in touch with one of our customer service team.