en español: Orina
The kidneys remove waste from the blood and make urine, also called pee. Urine is mostly water, so if you don't take in a lot of fluids (or if you sweat a lot), your urine has less water in it and it looks darker. If you drink lots of fluids, the extra fluid comes out in your pee, which looks lighter. Urine is stored in the bladder until it's peed out.