First, blot up any liquid by putting towels or absorbent rags over the spot and stepping on them. Start with gentle pressure and keep increasing it (right up to putting your full weight down) and changing to fresh rags or towels, until no more moisture is coming out. If the stain is fresh, apply a bacteria/enzyme digester (can be purchased at a pet store) according to directions -- it's the only way you can deal effectively not only with the stain but also the odor. Bacteria/enzyme digesters work well but they work slowly, so be sure to leave the solution on as long as it says. Urine has probably penetrated down into the carpet and pad, so use enough solution to reach as far down as the stain did. Apply the solution, put plastic over it, and step on the spot several times until the area is well saturated. Then, leave the plastic on the whole time the digester is working, to make sure the spot doesn't dry out. If the stain is old and dry, you may find it anywhere from hard to impossible to remove, but go ahead and try the bacteria/enzyme digester. Bear in mind that if it's a popular accident site you're treating, the bacteria may produce enough ammonia in the course of breaking down the stains to create a super-alkaline situation that interferes with their own action. In cases like this you may need to neutralize the spot after the bacteria have been working for about four hours. Mix up a solution of one cup of vinegar to a gallon of warm water. Rinse the area with this and then apply a fresh batch of bacteria/enzyme solution. If the stain is still there, you'll probably need to call in a professional deodorizing specialist. A complete cure will probably involve cleaning the entire carpet by extraction and replacing the pad underneath, if not replacing the carpet and sealing the hard-water, you'll need to use a phosphoric acid cleaner to remove the scale. Again, let the acid soak subfloor.