The voltage delivering 1 watt depends on how many amps are present. We use watts to measure power (P), and amps (I) times volts (E) equals watts.
The urea and water that make up urine are removed from the blood in  the kidney. This is then passed on to the bladder which will be  excreted as urine.
Since ammonia is not a healthy thing to have in high amounts in your body, it is processed by the body into urea. Urea is then carried in the blood to the kidneys where it is removed and filtered out in the urine. Blood Urea Nitrogen is an indicator of how much ammonia is being transferred into urea.