Unfortunately, carpets stain. Wine, cola, blood and makeup can all leave hard to remove stains on a carpet. However, who would have thought plain old water could actually stain a carpet? Well, it can. Small amounts of sediment dissolved in the water can be left behind when a water spot dries, leaving a tell tale stain. Happily, in most cases, a water stain is easy to remove.
Mix a solution of half water and half white vinegar. The vinegar is acidic and will neutralize the alkalinity of the sediment that is making the water stain.
Moisten a clean white terry towel with the water/vinegar solution.
Rub the towel gently over the water spot. The objective is to get the tips of the carpet fibers wet, not to soak the carpet itself.
Allow the carpet fibers to dry. Hopefully the stain is gone or at least minimized. If the stain is reduced but still noticeable, repeat the water/vinegar process until the stain is gone. Allow the fibers to dry between each application.
Water stains on natural fibers may produce what is know as "cellulosic browning," a stain that can only be removed by a trained carpet cleaning technician.
The most important thing you can do to stop your carpet from staining is react quickly to any spills. Blot up liquids with white paper towels or a clean absorbent cloth. Blot (don't rub) the spill and work from the outside in to the middle. Rubbing will just spread the stain over a larger area. Products that clean clothes will often clean carpets as well. A laundry pretreating product on a fresh spill will often prevent it from permanently staining.
Whenever you are trying to remove any stains from your carpet, always first test in an inconspicuous spot first.