In Minnesota we get lots of snow and ice so we use chemicals to melt ice on our sidewalks and roads. Those winter chemicals can build up on your carpet leaving distinctive white rings when it dries.
Have you ever looked at your boots half way through winter and noticed a white chalky substance? This is from the chemicals used on sidewalks, driveways and parking lots to melt snow and ice. These chemicals build up on your footwear and get tracked in on your carpet. Calcium chloride and sodium chloride, also known as road salt, melt the snow and ice on the road. They also promote corrosion and rust on your car, so you can imagine what road salt will do to the carpet in your home.
Road salt or sidewalk de-icer is gritty and when in chunks can collect on the bottom of your shoes and be tracked indoors onto your carpet. Add melted snow and ice and these chemicals dissolve, allowing them to invisibly coat your shoes and boots. In this liquid form they then soak into your carpet and then leave a crusty white ring when they dry. Add road sludge to the mix and now you have dirty brown or black stains.
The best way to prevent road salt stains on carpet is by removing your shoes before entering your home.
One of the easiest ways to encourage this is to buy a boot tray. Then either buy a small rug that will fit inside the boot tray, or use a dark towel that you no longer want or need. Place the rug or towel inside the boot tray. This will absorb the water from the shoes and boots, wick it away, and allow the water to evaporate. That way you won’t have as much dirty residue deposited around the tray when you put your footwear back on.