OK I Know dogs. My dog had the same problem. if the puppy is new to your house he could just be shy and might need more time to settle in but your dog could be sick so either way you need to check with the vet quickly
When a puppy stops dinking you need to get to a vet. Dehydration is a very serious thing especially for young puppy! Not eating for 24 hours isn't that bad, but not drinking is HUGE! Get to the vet ASAP!