Need a bit more info. When was it born, i.e. has the mother finished whelping and is there definitely no more puppies to come out?
If this is an only pup it will still only drink as much as it wants, and the bitches milk will gradually dry up. If the pup is not regularly feeding from each teat some may get blocked and she may get mastitis, so if any of her teats feel hot or look inflamed get her to a vet. Also give her a small amount of calcium now she is feeding or else she may get eclampsia.