Young dogs can have genetic kidney failure . . Your vets should insist on blood work and urinalysis. If they don't either insist on it or find another vet.
Drinking excessive water and peeing so much is not normal.
Just because pup looks good doesn't mean something is not going on. Friend had a gorgeous Sheltie pup, active and beautiful and was drinking a lot and peeing. Went to vet, had bloodwork done , pup was in acute kidney failure.
Insist on bloodwork or find another vet.