GRAF UK are specialists in underground rainwater harvesting. GRAF complete packages provide everything you need for professional rainwater harvesting. For use in the garden or home, suitable for pedestrian or vehicle loading - everything is possible!
GRAF's The Ultimate Guide to Rainwater Harvesting
They offer the Platin Tank (and Platin XXL Tank) and the Carat Tank (and Carat XXL Tank).
Tank sizes range from 1500 litres to 122,000 litres.