IF you suspect that your glider is dehydrated, perform the tent test.

Gently pull the skin between the shoulder blades up and away from the body.
Release the skin.
If the skin goes back into place quickly, the glider is NOT dehydrated.
IF the skin stays tented, then there is some dehydration.

Dehydrated gliders should be seen by a vet. If the dehydration is severe, the glider will require sub-q fluid injections. Dehydration is often a symptom of a greater concern. Always seek a vet's advice and intervention when a glider is dehydrated.