This statement is true. The kidneys play a role in waste excretion. In particular, the kidney helps the body get rid of waste nitrogen in the form of urea. The urea collects in the kidneys and is dissolved in water to be excreted as urine. But the kidney also plays a role in osmoregulation. This can be defined as the water and electrolyte balance in the blood plasma levels. The collection ducts in the kidneys collect excess water from the blood plasma to release as urine. If the water level is too low and the electrolyte levels are too high, the hypothalamus can trigger a signal to the pituitary gland to produce the chemical hormone ADH (antidiuretic hormone). ADH ultimately travels to the kidneys to bind to the walls of the water collection ducts, thus making the normally impermeable walls permeable to water. This allows water to pass through the walls of the collection ducts and be taken back up into the bloodstream, thus restoring the water/electrolyte balance in the plasma.
osmoregulation is an example of homeostasis. it refers to reguloating the water and salt content of the body. The kideys do regulate body water content. If the body water content is low and the blood is concentrated this is detected by the hypothalamus of the brain. A chemical called ADH is released from the pituitary gland and travels through the blood to the kidneys. The kidneys can reabsprb things like water through the walls of the nephron before the urine is sent off to the bladder. The ADH causes the walls to become more permeable and so more water is reabsorbed back into the bloodstrem making the blood more dilute. If the blood is dilute then no adh will be released and the walls will becom less permeable minimising the reabsorption of water back into the bloodstream and so the blood will become less dilute.