If you have ever purchased or rented a residential carpet cleaning machine, this information is for you. This equipment can be of a benefit for interim spot cleaning between professional cleanings. However, if your are not careful, the Do-It-Yourself machines can do more harm to your carpets than good.
If the machine's directions have you adding a shampoo to your water tank, I suggest not using it. The suction on these machines is not strong enough to rinse out the shampoo and as a result, will leave a residue on your carpet. The residue will then act as a big magnet pulling dirt from the bottom of your shoes. The result is you will have clean shoes and even dirtier carpets. Straight water is a good cleaning agent and should be used without any shampoo.
Over wetting of carpets is another potential problem. Depending on how wet the carpets get, the subfloor (especially if it is hardwood) can be damaged, carpet pads can prematurely fail due to getting wet and the carpet itself can be damaged and fail prematurely due to over-wetting. The impact of these issues shows up later by reducing the life of the carpets or seeing the damage to the sub floor when you replace the carpets. Also, if it takes more than 24 hours for the carpet to dry, then the possibility for mold and/or mildew to begin greatly increases.
Once again, if you decide to use a Do-It-Yourself carpet cleaning machine, be wary of adding a cleaning product to the reservoir and be careful of overwetting.