Is my dog injured, or infected?

I have a 13-year old, Husky mix, not neutered, male dog. He limps on his hind legs and does not move his tail. Moving his tail causes a lot of pain, enough to keep him immobile for long periods of time. He refuses to eat, but continues to drink water. I have also not witness him make any bowel movement, but he does urinate. The vet told me he might have what's called cauda equina syndrome. The vet also mentioned a possible infection. A week before I notice my dog's failing condition, I caught him drinking a puddle of rainwater that fell from the roof. The roof was recently replaced. So have you ever experience this with your dog?