Round Rainwater Tank Dimensions: 1900mm x 2020mm (RD-1900-2020). Kingspan's 5,500 Litre Tall Round AQUAPLATE Steel Water Tank is a popular size tank with a tall height. It is ideal for outdoor use, in gardens, pool top-ups and plumbing into toilets and laundry. AQUAPLATE is a BlueScope steel specifically designed for use in rainwater tanks and storing drinking water. The corrugated steel tank has an inner poly layer fabricated to a galvanised steel substrate, while the outer layer consists of a COLORBOND laminate coating.