Water Storage Tanks for Rainwater Harvesting and SuDS Attenuation

Aquality offer a range of water storage and attenuation tank systems that can accommodate different site conditions, and these include GRP, geocellular, large diameter pipe and in-situ concrete. Our technical design team are able to provide advice on the suitably of a tank dependant on site conditions.

Water storage tanks are an essential part of any rainwater harvesting system or a component in SuDS attenuation system , for smaller systems this maybe an above ground tank, or a free standing tank located in a plant room. For larger systems this is far more likely to be a below ground tank.

Any tank designed for use as a rainwater harvesting system that also uses surface water from hard standings must be able to be inspected and maintained. The residence time in a storage tank will be longer than for an attenuation tank, this inevitably means that there will be greater settlement of fine particles that will need to be periodically removed from the tank.

Below ground tanks are load bearing structures and therefore design needs to be undertaken by a suitably qualified engineer. There are many factors that will affect the choice of material used to construct the tank. Loadings both vertical and lateral need consideration, these include but are not limited to:

• Cover levels
• Buried depth of tank
• Soil type e.g. Clay, gravel
• Vehicle loads – static and dynamic
• Groundwater if applicable – floatation and hydrostatic pressure
• Proximity to buildings and other structures e.g. roads that might impose load or might be affected by the tank during and post construction.

These are preformed glass reinforced plastic (GRP) tanks  are available as complete units or as sections that can be assembled on site to form rainwater harvesting or SuDS attenuation tanks up to around 30m3. The tanks conform to BS EN 976 & BS EN 13121, and where used as part of  a rainwater harvesting system meet the requirements in BS8515.  Aquality offer both buried and above ground sectional GRP tanks in a variety of sizes.

Are plastic modular units widely used in the construction industry due to their flexibility of design and relative low cost. There are a wide variety available on the UK market but for use in a combined rainwater harvesting and SuDS attenuation system. Aquality only offer a system that:

• can be fully inspected to the extremities of the construction and maintained with the use of remote CCTV and jetting equipment.
• are designed to CIRIA C680 or C737
• carries a relevant BBA certificate

Geocellular tanks have limitations on overall buried depth and cover level dependant on loadings and are not as easy to maintain as other types of tank and are perhaps better suited to smaller scale applications or where footprint is restricted.

An essential component for any geocellular unit is the geomembrane lining and its installation as this is ultimately what holds the water in the tank and prevents it from leaking. Geomembranes need careful selection and installation should be carried out by a suitably qualified lining contractor. For further information on our lining services and materials please click here.

Large diameter plastic pipes, are available in a variety of materials, at Aquality we offer composite steel re-inforced plastic (CSR). The pipe is available in ten diameters from 900mm to 2250mm,. The pipes are push fit spigot and socket pipes, and are supplied in 3.0m or 2.6m  lengths for use in standard trench boxes. Alternative lengths are available to order.

It is essential that any rainwater harvesting or SuDS attenuation tank is completely watertight, the CSR pipes can additionally be internally welded as secondary sealing measure if required, this maybe important in situations where the water storage tank is in groundwater.

The  Aquality CSR system also carries:

• WRc Approval
• Various Water company approvals.

Concrete tanks can either be precast or in-situ cast and are structurally the strongest water rainwater harvesting or SuDS attenuation tanks available. Where cover levels are minimal or other site considerations rule out other options then concrete maybe to obvious choice.

Aquality offers Goliath an in-situ cast solution using a sacrificial form-work system that creates the roof structure of the tank. The tank should be designed to Eurocode 2 whilst taking into account Eurocodes 1 and 7. Such tanks should ideally be constructed to Sewers for Adoption standard and comply with CESWI regulations.

The Goliath system is available 500mm – 2500mm in height as standard, and a shallow high strength formwork system is available for heights less than 500mm