Do you have a dripper for him? He might be a shy drinker and just not drinking in front of you... Best way to know if he is getting enough water is to check his urates (white part of poo). If it's white, he's drinking enough but if it's yellow or orange, he is dehydrated. Also, sunken eyes is a sign of dehydration.
I'm a new owner but I got an idea... find syringe, fill with clean water, inject water into the worms he eats? Dunno if he would eat them cause they might die, but it's prob worth a SHOT, get it... lol.
do what i do when my big guy wants to hiss i spay water in his mouth he keeps it open and doesn't his when i'm done spraying he closes his mouth and goes on his merry way. thats one way to get him water. also my panthers and baby vieled will drink like once a doy and i mist them three times a day or everyother day depending on their moods and they are all growing fast they will drink when they want to.
ask a diabetic. prob pharmacy? walgreens? i've heard lots of clinics offer free syringes to drug users so they don't pass on diseases. btw not trolling, i mean your cham's life is on the line.. i'd go into a clinic and just ask where i could get a syringe. I just now googled it and apparently you can go to your local department of health and get one. But otherwise.. a vet? I'm sure they would oblige. I don't know how much a saline iv would cost for them to do, but i've heard of them done on dehydrated chams.