yes it could be due to him coming from a shelter and having a nervous habit from there being around all of the stress that comes with being in a shelter, and yes it too could be from dehydration! both very possible! i have a female dog that does that now when she is hot and needing a drink of water i would say it may be a way for them to cool off their mouths since their mouths are a way for them to keep cool! panting cools them down. so maybe wetting their mouths with saliva may also help them to cool down! i agree there are many reasons why he could be doing this. if you are fearful that it may be causing him harm or to be uncomfortable then you should call and ask a vet if they say to bring him in then go ahead and make an appointment. when the appointment comes around have him in his normal environment (alone, water or no water, caged or not caged- whatever his normal environment is) before you take him in so that when he begins to act in this way the vet will be able to see first hand what the issue is then he will be more inclined and have a better idea on how to help your doggie out! in my experience i would have to say its nothing to really stress over. i hope this helps! good luck to you and your family!
p.s. i have also noticed that if you give a dog gatorade (any color) if the dog drinks it theres a problem a vet should see, if the dog deos not drink it theres no problem! on some dogs it works on others i may not but its worth a try!
p.s. i have also noticed that if you give a dog gatorade (any color) if the dog drinks it theres a problem a vet should see, if the dog deos not drink it theres no problem! on some dogs it works on others i may not but its worth a try!