My dog is drinking and is still dehydrated

There is a bottle of water that you can get in a pet supermarket that it's to prevent dehydration. Or to give to animals when they are dehydrated. I hope this helps.

How do you know the dog is dehydrated?

She is an old dog and know matter how much she drinks she still acts like she has not a drink in a week and we keep her water bowl full it is never empty

Ah, she is an old dog.

Have you taken her to the vet? One of the signs of either thyroid problems or diabetes is the animal hanging around by the water bowl and can't seem to get enough water.

No I have not but she is also not my dog I will tell my friend, so they can get her to the vet.

No I have not but she is also not my dog I will tell my friend, so they can get her to the vet.
That would be your friend's best move. I think a blood test will give accurate information about the dog's condition.

Has the dog lost weight? Does he pee a lot?