It all depends on the situation. In some situations where carpet has been wet for an extended period, water damage will cause what is called delamination (the backing separates from the fibers) and will usually require replacement. Or if the water was from a non-clean source like sewage, the carpet will most likely need to be replaced. But in most cases, if carpets were saturated by clean water, and if we get to them right away, they can be dried, sanitized and cleaned without damage.