My first suggestion would be to get him started on some canned food as it has more moisture which will make his urine less concentrated. You can also add water to the canned food. You can try to boil some skinless/boneless chicken and see if he is willing to drink that "broth" once it has cooled. I don't think that lemon will do the trick, plus it is very acidic. If your vet says it is ok, then you can give it a try. If his urine is too acidic, he could develop a type of crystals. I would have his urine checked first to see what the PH is. If your vet thinks he can have lemon in his water daily, and he likes it, by all means, go ahead. Is there anything else I can help you with?