Hot Water Extraction, aslo known as "Steam Cleaning" is the method recommended by the carpet manufacturerers as outlined on Shaw Industries website.
This process consists of initially spraying a solution of water and detergent into the carpet pile to emulsify the embedded soils called "pre-spraying" then rinsing back out the broken down soil, detergent and excess water with hot water and a powerful vacuum into a holding tank. This can be done from a truck-mounted unit outside the home (very powerful) with only the hose and floor tool brought inside, or by a portable system brought into the home or office (old system and not so powerful). The truck-mounted system is preferred because the dirty air and humidity are exhausted outside rather than a portable unit re-circulating humidity inside the home. Plus, the power of the truck-mounted unit has far more capability to extract more soil and clean with more heat allowing for quick evaporation. Fibers dry much more quickly than portable units.
Truck-mounted steam extraction is the sole method 95% of all carpet manufacturers and carpet fiber producers acknowledge as a viable cleaning method to uphold their warranties when the work is done by a certified and "listed" professional with the IICRC. 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. In fact, all other methods void manufacturers warranties as they actually damage fibers. They found out that steam cleaning with a truck-mounted unit adds restorative value to fibers that will extend the expected life and resiliency as much as 50% and allowing manufacturers to add years to the life of their product when properly maintained.
Other points of interest:
The term "Steam" is a misnomer since the temperature required to generate steam is never achieved (240° F) and would actually delaminate the carpet fibers from the backing. The recommended temperature is 180° to 190° F, and most truck mounted equipment manufacturers are able to maintain this standard.
Steam cleaning 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.
It is a very detailed cleaning having the ability to get along edges of walls, over steps, behind toilets or large plants, and most times under furniture without having to move a thing and no risk of damage.No other method has the specialty tools nor the capability to do those things.
The steam cleaning extraction method is the only method that can rid there cleaning agents because they have the ability to extract them away.
Another popular fact is that the heat of the water used to extract (180-190 degrees) the soils and pre treatment detergent residues acts as somewhat of a sanitizer for certain bacteria (most die in temperatures over 120 degrees) and will also kill carpet mites, ants and like on contact.