Try the rice with plain boiled chicken meat or hamburger with the fat drained off. No puppy food at all as that can be a bit harsh with a tummy upset.
I suggest bringing a stool sample to the vet to be checked for worms, coccidia, or giardia as your pup may need meds to get over this.
You can also try giving plain pedialyte instead of water and adding some cooked sweet potato or canned pumpkin to the food as the fiber in those can help absorb fluids to slow diarrhea down.
You go back to regular food by slowly adding in dog food when the pup is better.
If he has not had all his shots this could be from a viral disease too. Rule out parasites first but if this is parvo then ask the vet about using the new human antiviral med Tamiflu which you can read about here
www.marvistavet.com/html/body_oseltamivir.html
Hope this helps you!
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