The kidneys are amazing with so many important functions. Sometimes we do not fully appreciate its value until we see someone that is has a dysfunctional kidney.
Each kidney has about 1million nephrons which filter and reabsorbs the blood. The kidneys maintain normal arterial pressure (or increase BP as needed for compensation), hydration, they manage electrolyte balance, get rid of toxins and waste products the kidneys also act as a buffer for some of the cellular byproducts.
About 180L of fluids are filtered by the kidneys every single day!