501-15000Litres

For a typical household rainwater harvesting system, 2,000 - 5,000 litres usually covers garden use and WC flushing for an average property. Larger sizes towards the top of this range suit commercial premises, livestock watering, fire suppression reserves or off-mains drainage systems serving several properties. If you're unsure, tell us your daily demand and roof catchment area and we can help you work out the right capacity.

Polyethylene (poly) tanks are lighter, generally more cost-effective and well suited to straightforward above or below ground water storage. GRP (fibreglass) tanks offer greater structural rigidity, are often preferred for larger below-ground installations or where ground conditions are challenging, and can be manufactured to bespoke shapes. Both materials are available WRAS-approved for potable water where required — the right choice depends on your installation method and site conditions.

Yes, many tanks in this range are designed for underground installation, particularly for rainwater harvesting, septic and sewage treatment applications where a discreet, space-saving solution is needed. Below-ground tanks need a properly prepared, level base and correct backfill material to avoid flotation or deformation — check the manufacturer's installation guide before digging. Above-ground versions are also available and are simpler and cheaper to install where space and aesthetics allow.

Most tanks over 500 litres need a level, well-compacted base — typically a concrete slab or well-compacted pea shingle bed, depending on the tank material and whether it's above or below ground. Ground conditions, water table and tank weight when full all affect the specification, so it's worth checking site-specific requirements before delivery. Getting the base wrong is one of the most common causes of installation problems, so don't skip this step.

Tanks used for off-mains drainage, such as septic tanks or sewage treatment plants, fall under Building Regulations and the General Binding Rules for small sewage discharges, and you may need Environment Agency registration depending on the discharge point. Straightforward water storage or rainwater harvesting tanks usually don't need planning permission if installed within normal permitted development rules, but it's worth checking with your local authority for larger or above-ground installations. We're happy to point you towards the relevant guidance for your specific use case.

Tanks in this size range are usually delivered on a flatbed or crane-offload vehicle, so you'll need suitable access for the lorry and a clear, accessible unloading point close to the installation site. Larger tanks often can't be manhandled into position, so having a forklift, telehandler or crane on site for the day of delivery is strongly recommended. Check the exact dimensions and weight against your access route and site plan before ordering to avoid delivery day surprises.