Water Stains Under Carpeting
Water stains underneath the carpeting are usually bad
news and represent water damage. Once the carpeting is wet, your number
one priority is to dry the carpeting and padding out as soon as
possible. If you pull the carpeting up to dry it out, remember that it
will need to be reattached to the tack strip within a few days.
Now think for a second, if the carpeting is wet, try to figure out what caused the damage. If you have a roof leak and it's raining outside, your number one priority isn't going to be the carpeting, it's going to be patching the roof leak.
When the carpeting is wet, it can expand a little bit and then start to shrink once it has dried out. Once the carpeting starts to shrink, you could be in trouble. You will need to contact someone who can re-stretch the carpeting if possible. If the carpeting has contracted to much, it might need to be replaced.
Usually the water stains underneath the carpeting don't go away. This won't be a problem and you usually won't be able to see them from above. If the carpet stains are starting to turn black, you could have a mold problem. Especially if the carpeting was in dried soon enough.
If you have a dog and your carpet smells, there's a good chance that he's peeing on top of the carpeting and this could cause staining underneath.