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The natural product of the body’s waste processing system, urine is sterile when produced by a healthy body. It loses that sterility upon expulsion from the body, though. The first contamination can come during the urination process, when urine picks up bacteria living in the epithelial cells that line the urethra. Upon leaving the body, urine’s sterility can also be compromised by bacteria present in the air as well as in the collection container. In fact, since naturally-occurring sterile environments are virtually non-existent, once urine has left the body, it almost immediately loses its sterility.
When it’s said that urine is sterile, what’s meant is that it contains no bacteria or other living organism, or their spores. This is the case with urine when it’s first produced and is being stored in the bladder prior to expulsion from the body. What’s sometimes overlooked is that a sterile substance such as urine is quite capable of supporting or promoting life. In fact, the urea in urine makes it attractive for agricultural applications, although it must be diluted before it can safely be applied.
Urine’s main ingredient is water, comprising about 95% of the liquid by volume. The remaining 5% is composed primarily of urea, an organic substance produced by the body which is instrumental in removing excess nitrogen from the body. Chloride, sodium, potassium and other organic and inorganic compounds and dissolved ions are other substances found in urine, usually in minute quantities.
The composition of urine may be altered if produced by a body with a disease or medical condition. Diabetics’ urine, for instance, may contain a significant quantity of glucose. Likewise, the ingestion of certain foods or medications can have a short-term impact on urine’s appearance, especially its color. Even in these cases, however, urine is sterile. The main medical condition in which urine might not be sterile is a urinary tract infection (UTI), where microorganisms might contaminate the urine in the bladder and render it non-sterile.
The question of urine’s sterility invariably leads to questions about its suitability for drinking. Especially when urine is sterile, it’s perfectly safe to drink, particularly in limited quantities. Since urine is composed primarily of water and waste products from the body, it has little, if any, nutritional value. While in emergency situations drinking urine is an acceptable method of hydration, repeated drinking of urine, especially one’s own, involves putting back into the body those waste products the body is trying to eliminate. This will ultimately put an excessive strain on the kidneys, which are responsible for processing waste in the body.
The high water content of urine can be processed and reclaimed as potable water. The International Space Station’s waste processing systems are certified to process mammals’ urine for this purpose. This is a valuable resource in an environment like a space station, where there’s no renewable source of fresh water. The reclamation project processes not only the astronauts’ urine, but also that of the lab animals on board.