To me, as long as you're drinking a bottle of water with it I see no harm. You get hydrated from coffee. Of course you need to drink water in general, but the concept of drinking cups of water to balance out dehydration from coffee is just a myth.
Reptiles do not maintain their own body temperature within a narrow range like mammals and birds, so controlling their environmental temperature is critical for normal activity and good health. Reptiles are poikilothermic-which means that their body temperature alters with the surrounding environmental temperature.
A snake of any given weight eats far less than does a mammal of the same size because snakes are cold-blooded. A mammal must eat more in order to generate enough energy to maintain its body temperature. A snake only uses about 10 percent of the amount of energy used by a mammal of similar size.