Many individuals and communities worldwide are diverting and using urine for several reasons

• In wastewater, urine accounts for most of the nutrients — as much as 90 percent of the nitrogen and potassium.
• These nutrients can get into groundwater and lakes, rivers, and streams where they can pollute by over-fertilizing aquatic plants.
• The nitrogen in urea is quickly converted to ammonia, which is toxic to composting microbes and causes odor.
• The fertilizer value is lost when the ammonia in it evaporates and escapes up the exhaust pipe. For that reason, some might overestimate the nutrient value of composted human excrement.
• Urine adds more water than is necessary to compost feces and toilet paper. The moisture content of the feces (66 to 80 percent), plus the addition of toilet paper, is sufficient for good processing.
• The excessive salt (sodium chloride) we put in our foods is excreted in urine. Salt is toxic to living organisms in amounts above their minimum requirements and can inhibit the composting organisms. Further it can turn into “salt concrete” in locations where removing it is difficult and can “gum up” the composter’s mechanisms.
• Oxidized and diluted, urine makes a good liquid nutrient for plants.
• Although most of the nitrogen is either drained away as leachate or evaporated, it would require significant amounts of carbon (25 parts of carbon for one part nitrogen) to provide the optimum ratio to convert the nutrients in urine to a plant-available form. For some systems, that would require wheelbarrows full of additive.
• Several studies validated the collection and use of urine to fertilize crops, such as wheat, corn, and oats.
• Urine is usually sterile in healthy populations.
• Urine is portable and easy to collect separately and drain away.
• Urine mixed with feces produces a malodorous compound — worse than each of its components alone.
• When urine is combined with feces, certain malodorous compounds form, which do not form if they are kept apart. The bacterium, Micrococcus urea, is the responsible culprit.
• However, collecting and using urine presents some challenges:
• The urea in urine degrades rapidly to the gasses ammonia and carbon dioxide, unless it is contained or directly utilized.
• Urine contained without air will smell bad.
• Urine can be diluted and immediately used on plants. When it is used immediately, however, it has not been transformed into a plant-available form; one is relying on the soil microbes in the plant bed to do that. To preserve all of the fertilizer value of urine, it needs to be oxidized or composted. (an aerobic process.). For this, a carbon-urine mixture requires a carbon-to-nitrogen ratio (C:N ratio) of one part urine to 25 parts carbon to convert all the nitrogen to nitrates by aerobic soil bacteria. Nitrate is the form of nutrient that is available to plants.

Our bodies keep urine separate naturally, so we can collect and use it separately. Urine-diverting toilets which feature a urine collector and drain cast into the front of the toilet bowl opening, make urine collection as easy as using a flush toilet.