The kidneys filter the blood and remove extra water-soluble vitamins from the body. Water-soluble vitamins are absorbed in the intestines and delivered to the kidneys via the circulation. The kidneys filter these vitamins from the blood and excrete them in the urine. The majority of water-soluble vitamins are eliminated this way.
Small amounts of water-soluble vitamins can be excreted through sweat. However, the amount of vitamins excreted in sweat is generally much lower compared to urinary excretion.