Obviously not allowing your dog to get dehydrated is the best policy, but it's important to know the symptoms just the same.
* Loss of skin elasticity- if you pull up skin on your dog's back, it SHOULD spring right back. If it stays raised...that's a sign of loss of elasticity and dehydration.
* Dr or sunken in looking eyes
* Mouth and gums are dry and tacky. Hydrated dogs have a lot of moisture in their mouths. If you press your finger on your dog's gums and it doesn't go from white right back to pink, that's a bad sign.
* Dry nose
* Excessive panting
* Lack of appetite
It's important to contact your vet and rehydrate your dog slowly. You don't want to give endless amounts of water to be gulped down. This can absolutely make your dog sick. Giving small amounts of water, in short intervals, or allowing your pup to lick a few ice cubes until their hydration returns is best.