"Pooling' and 'watermarking' are forms of pile reversal that can change the appearance of both wool and synthetic carpets. This is a very aggravating problem that can occur in any carpeting at any time in the carpet's life. Even the best and most expensive carpets can pool. Unfortunately it is irreversible and permanent. We have even used the hottest water temperature (the industry standard used to take out 'crush marks' in carpets) on these areas and they will still persist.
In essence, pooling, or 'watermarking', is when the carpet's yarns are laying down in one direction and adjacent to that area the pile will lay down in a different direction creating a distortion in appearance – and an ugly one at that! In case you are wondering, carpet cleaning does NOT cause this. Notably, even if your carpet is fairly new and this pooling or watermarking occurs, most carpet manufacturers do NOT recognize this as a manufacturing problem and will not warranty against this.
There is no known explanation as to why some carpets pool in some homes and not in others. The most popular theory for this phenomenon is electromagnetic currents under particular homes, as it has been noted that there have been instances where someone could purchase a carpet that was on display at a distributor, for example, and then take the rug home and have this occur, only to have them buy a completely different carpet and place it in the same place and have the same thing happen.
Note: Pooling usually only occurs in cut pile carpets, not looped Berber carpets.