Filtering the blood is the primary function of the kidney. Every day the kidneys process about 200 quarts (190 liters) of blood and filters out about 2 quarts of waste products and extra water.To effectively handle this volume of blood, the kidneys are equipped with lots of blood vessels.iltering the blood is the primary function of the kidney. Every day the kidneys process about 200 quarts (190 liters) of blood and filters out about 2 quarts of waste products and extra water.