The urinary system has a fairly simple job. The kidneys filter the blood, then flush the filtered-out wastes (in liquid, of course) down through the ureters into the bladder. The bladder simply holds this liquid waste so it can be eliminated all at once, through the urethra. As you can probably imagine, this task of filtration, though simple in principle, calls for a highly-complex orchestration of goings-on within the kidneys!
It isn’t only pure wastes the kidneys filter out, though. They also help maintain a proper electrolyte balance and level of hydration by eliminating — or not eliminating — minerals and fluids, as needed. In similar fashion, they also help maintain a proper pH balance in the body.
Healthy urine should be light yellow to clear in color. If it’s very dark, that likely indicates a shortage of fluids in the body. Among numerous other problems (did you know mild dehydration can even impact your mood?1), too little fluid passing through the kidneys can enable minerals to precipitate and form crystals (that is, kidney stones) rather than being flushed through. It should not be dark, cloudy, or contain blood. It also should not carry an unusual odor. (Certain odors may be hints of systemic problems.)
However, do note that certain foods or supplements may cause strange colors or odors in the urine; in this case, these are not cause for worry. B vitamin supplements often produce a neon yellow color, sometimes tending toward green. Phenazopyridine, a medication often prescribed to address urinary tract pain, can turn the urine yellow. Consumption of asparagus may result in a strange odor to the urine.
Normal urination should also not induce itching or burning — these are signs that something’s not quite right.