Why should urine be treated as soon as possible?
Left untreated, you may wind up with a difficult to remove yellow stain, or worse, a dye loss. Over time urine salts become highly alkaline, and can bleach out your primary carpet dyes, starting with the weaker red and blue dyes, so that you are left with a yellowish or off white discoloration. At this point, your only options are to dye, or section (patch) the carpet.
