This method is often call "Warm Water Extraction", "Hot Water Extraction", or "Steam Cleaning" and is the cleaning method nearly all carpet manufacturers and carpet fiber producers recommend.
This is the only cleaning method classified as "deep cleaning". All the others are considered "light surface cleaning" because they are incapable of removing soil deep in the pile. Also, all other methods leave large amounts of cleaning agent in the carpet after cleaning.
The maintenance brochure published by the world's largest carpet manufacturer, Shaw Industries, recommends this method because its own research indicates that it provides the best capability for cleaning.
This method is frequently called steam cleaning due to the fine spray of water used to force dirt out of the carpet which is sucked up by the vacuum slot immediately in front of the spray. Seldom is real live steam used, however. This process consists of spraying a solution of water and detergent into the carpet pile and recovering the water and soil with a powerful vacuum into a holding tank. This can be done from a truck-mounted unit outside the home with only the hose and floor tool brought inside, or by a portable, system brought into the home or office.
From a health standpoint, the truck-mounted system is preferred because the dirty air and humidity are exhausted outside rather than recirculated around the house. Additionally, truck-mounted systems usually are more powerful than portable units and do a much better cleaning job and get the carpet dry more quickly.
With some truck-mounted systems (called PTO's), the vehicle itself must run in neutral during the cleaning and in many others a separate engine (sometimes with a propane or oil-fired heater) is used to power the unit and heat the water. In both cases, the van must be parked well away from the house and positioned so that exhaust fumes do not enter the house. All-electric systems, such as the Bane-Clene® systems, do not have this problem.
Depending upon the equipment, temperatures may range from cold tap water to boiling hot water and even super heated water over 200 degrees F. Of course, with extremely high temperatures, there are dangers of scalding should a solution line break.