This document provides information about the kidneys and their function. It states that the kidneys are bean-shaped organs about 4-5 inches long located near the lower back that filter waste from the blood. The filtering units are called nephrons, which help pass out waste and metabolize nutrients. The kidneys keep balance of salts and other substances in blood and produce hormones. They remove urea and metabolic waste like water, salt, and nitrogenous waste from the blood. The document also lists ways to keep kidneys healthy like drinking water, exercising, and eating a balanced diet.