Obligatory reabsorption of water occurs in the kidneys. The reabsorption of water is a part of the process that the kidneys perform of filtering and returning to the bloodstream about 200 quarts of fluid within a 24-hour period, states the National Kidney Foundation.
During the process of filtering and returning fluid to the bloodstream, the kidneys are producing urine, explains the National Kidney Foundation. From the 200 quarts of fluid filtered, about two quarts are excreted by the body in the form of urine, while the other 198 quarts return to the body, or are reabsorbed. The filtering process enables the body to balance the chemicals within it.