Blood in your urine is called hematuria. The amount may be very small and only detected with urine tests or under a microscope. In other cases, the blood is visible. It often turns the toilet water red or pink. Or, you may see spots of blood in the water after urinating. There are many possible causes of blood in the urine. Bloody urine may be due to a problem in your kidneys or other parts of the urinary tract, such as: 1  Cancer of the bladder or kidney.  Infection of the bladder, kidney, prostate, or urethra.