The kidneys are like a very complicated filter. Blood is filtered through the kidneys. Impurities are removed and dissolved in water. This waste water is sent to the urinary bladder.

To work properly, your kidneys need plenty of water. Sometimes people feel a soreness in their lower backs because their kidneys do not have enough water to function properly.

When a person's kidneys quit working, they can use a dialysis machine to filter their blood. They must pass their blood through the machine several times a week. This machine is not as good as real kidneys, but it will keep your body functioning.