What type of water helps hibernating bears stay hydrated while they do not drink?

The type of water that keeps hibernating bears hydrated without drinking is metabolic water. It is water produced inside the body during chemical reactions, especially as stored fat is broken down for energy.

During winter dormancy, bears generally do not eat or drink. Their metabolism slows, but it does not stop, and oxidation of fat supplies both energy and enough internally generated water to meet their needs. This is why “metabolic water” is different from glacial, saline, or capillary water: those are environmental or biological water categories, not the key source described in bear hibernation.

Bear hibernation was once disputed because bears’ body temperatures fall less dramatically than those of many small hibernators. Research on black bears in 2011 and brown bears in 2016 helped confirm that their prolonged winter state is genuine hibernation. Bears also conserve water by avoiding urination and recycling nitrogenous waste, allowing them to remain in dens for months without normal drinking or feeding.