How do we control the concentration of urine?

Osmoregulation is the homeostasis of water in the body. It is important that water volumes are kept relatively constant as this influences electrolyte concentrations and cell activity.
There are many ways in which we can control the content of water in our body. One way of retaining water is by reducing the amount lost in the urine.
Osmoreceptors in the hypothalamus detect when water levels are low, by detecting changes in the concentration of electrolytes (primarily sodium). The hypothalamus responds by triggering the release of antidiuretic hormone (ADH). ADH acts on the collecting ducts of the kidneys, allowing reabsorption of water and reducing the volume of urine excreted.