Composition
Exhaustive detailed description of the composition of human urine can be found in NASA Contractor Report No. NASA CR-1802, D. F. Putnam, July 1971. That report provided detailed chemical analyses for inorganic and organic constituents, methods of analysis, chemical and physical properties and its behavior during concentrative processes such as evaporation, distillation and other physiochemical operations. Urine is an aqueous solution of greater than 95% water, with the remaining constituents, in order of decreasing concentration urea 9.3 g/L, chloride 1.87 g/L, sodium 1.17 g/L, potassium 0.750 g/L, creatinine 0.670 g/L and other dissolved ions, inorganic and organic compounds.
Urine is sterile until it reaches the urethra, where epithelial cells lining the urethra are colonized by facultatively anaerobic Gram negative rods and cocci. Subsequent to elimination from the body, urine can acquire strong odors due to bacterial action, and in particular the release of ammonia from the breakdown of urea.
Some diseases alter the quantity and consistency of urine, such as diabetes introducing sugar. Consuming beets can result in beeturia (pink/red urine containing betanin) for some 10–14% of the population.
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