Truck mounted steam cleaning, AKA hot water extraction, is the industry standard. It is the most widely recommended cleaning method by the major carpet manufacturers. The Institute for Inspection Cleaning and Restoration(IICRC) lists it first in the S100 Carpet Cleaning Standard.
All other methods, though viable are subordinate to steam cleaning. Because of the high pressure achieved with this process, Pollutants, bacteria and allergens are flushed away. The high temperature also aids to sanitize carpet. A balanced pH is reached after the final rinse. Drying takes usually 4 to 8 hours.