We present the generalised supergrowth of single and double walled carbon nanotubes like "water assisted supergrowth" at low temperature (630 degrees C) and pressure (1 Torr) by chemical vapour deposition using various thicknesses of iron supported alumina substrate as a catalyst. Reduced temperature and low pressure synthesis of single walled (SW) and double walled (DW) carbon nanotubes is of interest for their efficient growth into device architectures. Pure SW with 2.5 nm diameter are obtained with 0.37 nm Fe catalyst at 630 degrees C. We demonstrated the decrease of the density versus temperatures and also obtained high density materials (1.4 x 10(12) cm(-2)) at low temperature (580 degrees C). Scanning and transmission electron microscope studies provided information on the height, density of the carpets and the structure and diameter of SW and DW carbon nanotubes, respectively.