Urine consists of 95% of water, 2.5% of urea and the remaining 2.5% is a mixture of minerals, salts, hormones and enzymes. Only urea , the substance after which urine is named, can be poisonous when present in the blood. However, this is irrelevant in the practice of drinking urine, as urine is not immediately put back in the bloodstream. In small amounts urea gets back into the body, it is purifying, and clears up excess mucus. Urine is entirely sterile after secretion and has an antiseptic effect.
One of the liver's most important functions is detoxification of the blood. The liver removes poisonous substances from the blood and either stores them or secretes them into the gall bladder. In the latter case, the poisonous substances end up as bile in the intestinal canal. They then leave the body in the form of defecation. After the blood is detoxified by the liver, it flows to the kidneys.
The kidney's most important function consists of balancing out all elements in the blood. They remove all superfluous vital substances from the blood, and filter out a surplus of water. This water and the vital substances consequently form urine. In order to save energy and bring the blood into balance, the kidneys remove unused enzymes from the blood. The same goes for hormones, minerals and other substances. It is clear that urine is full of vital elements, which can hardly be called waste products.