You already have good answers but here is another explanation. It is from
http://www.shirleys-wellness-cafe.com/urine.htm
Healing with Urine Therapy
Urine is not a dirty and toxic substance rejected by the body. Urine is a by-product of blood filtration, not waste filtration. Medically it is referred to as "plasma ultrafiltrate". It is a purified derivative of the blood itself, made by the kidneys--whose principal function is not excretion but regulation of all the elements and their concentrations in the blood. Urine can be compared to leftovers from a meal, and this metaphor may help us understand why our bodies excrete elements that are valuable to our health and well-being.
Nutrient-filled blood passes through the liver where toxins are removed to be excreted as solid waste. Eventually, this purified "clean" blood undergoes a filtering process in the kidneys, where excess water, salts, vitamins, minerals, enzymes, antibodies, urea, uric acid and other elements not usable at that time by the body are collected in the form of a purified, sterile, watery solution that is urine. The function of the kidneys is to keep the various elements in the blood balanced. The important elements in the blood are not filtered out because they are toxic and harmful to the body, but simply because the body does not need a particular concentration of an element at that specific point in time. It is this very regulating process of the kidneys that allows us to eat and drink more than our bodies need at any one time.
Urine is considered to be an invaluable source of nourishment and healing that perhaps has been too controversial or not financially rewarding enough for it to be talked about and encouraged as a potent medicine. One's own urine, a living food, contains elements that are specific to one's body alone. The body is constantly producing a huge variety of antibodies, hormones, enzymes and other natural chemicals to regulate and control its functions and combat imbalances that one may not be aware of. Biomedx.com
Clinical studies have proved that the thousands of critical body chemicals and nutrients that end up in urine reflect the individual body's functions. When re-utilised, these chemicals and nutrients act as natural vaccines, antibacterial, antiviral and anticarcinogenic agents as well as hormone balancers and allergy relievers. The information that urine contains therefore cannot be duplicated or derived from any other source. Just as nature produces no two people who are exactly the same, there are no two urine samples in the world that contain exactly the same components.
Urine therapy reviews Don't take this therapy lightly. Multiple sclerosis, colitis, lupus,
Rheumatoid Arthritis , cancer, hepatitis, hyperactivity, pancreatic insufficiency, psoriasis, eczema, diabetes, herpes, mononucleosis, adrenal failure, allergies and so many other ailments have been relieved through use of this therapy. After you overcome your initial gag response (I know I had one), you will realize that something big is going on, and if you are searching for health, this is an area to investigate. There are numerous reports and double blind studies which go back to the turn of the century supporting the efficacy of using urine for health.
http://www.urine-therapy.org
is a growing online community connected by our curiosity about urine therapy. How could something so simple make such a profound changes in peoples' lives? Does urine therapy have scientific evidence to support it? Is it just a wacky idea practiced by crazy nut jobs? You can decide here, as a member of this site.