Fluid balance in the body is impacted by several organ systems, but the kidneys control how much water is retained or expressed in the urine. The lymphatic system contributes to water balance in the body by collecting excess fluid and returning it to the venous system. The skin is a source of water loss through evaporation, even without sweating. Water is lost in exhaled air from the lungs. The hypothalamus in the brain secretes hormones that regulate blood osmolality and blood volume, ie, the amount of water present in the bloodstream.