Human Urine formation helps to maintain the balance of minerals and other substances in the body. For example, excess of calcium is normally eliminated through the urine. Urine also excretes ammonia, the build-up of which is harmful to the body. Human urine is the result of a mechanism that maintains the appropriate amount of water in the body. When it leaves the body, Human urine is usually around pH 6, though it may be as low as 4.5 or as high as 8.2. As urea, the compound which accounts for 75-90% of the nitrogen in urine begins to decay, hydroxide ions form, raising the pH as high as 9-9.3. The decay of urea into carbon dioxide is catalyzed by urease.