My yorkie was also a very big water drinker
But even that is not enough water for them. I couldn't believe it either, but it's very true. My yorkie has been stone free for over 1 yr now because of switching him to a homemade diet that is very high in moisture.
I would love to recommend a food, but the truth is that the type of food will *completely* depend on what type of stone your baby had. If it was calcium oxalate, it would require a completely different type of diet than what ammonium urate would require. This is why it's really important for your vet to analyze the stone. If it's too late for that, then maybe he could do a urinalysis to check for crystals and to check his urine pH. The crystals and pH may give some insight into what type it was and what diet would be required. Calcium oxalate stones *tend* to form in alkaline urine and require low oxalate diet. Ammonium urate stones form in acidic urine and require a low purine diet and liver friendly diet since it's seen mainly in dogs with liver disorders. Foods that may be okay for ammonium urate stones may not be appropriate for dogs with calcium oxalate stones and vice versa. If it's struvite stone, your baby would benefit from something like Berry Balance by Solid Gold.