Water by itself is a solvent but again by itself a poor cleaner by itself. As for capillary characteristics in cleaning I have never heard it used in description of cleaning process. As you might guess I am a cleaner who has spent a lot of time studying the science of cleaning. I'm not opposed to natural cleaning products or do it your-self cleaning. What does bother me in the rug business is old wise tales about handling rugs the likes of which you have mentioned with little or no factual basis.
Lets make clear.
I am not objecting water itself is not a proper cleaning agent for rugs, particularly for chemical dyed rugs. Why dont we use only a chemical additivies to clean such rugs if water is not a good substance. It is difficult to explain this. This is their menthality and think that they are wise people. But they forgot simple, basic things.