Our bodies manage millions of chemical reactions every day. These reactions depend on the concentration of the fluid in our cells and our blood being tightly controlled all day, every day. How does it do this? By making us thirsty, for instance, when the fluid is tending to become more concentrated and making us pass more urine when it's getting less concentrated.
This is a companion discussion topic for the original article at https://patient.info/treatment-medication/osmolality-osmolarity-and-fluid-homeostasis-leaflet