Thank you for your patience. These symptoms are definitely concerning, particularly given your boy's age. As you can probably appreciate, there are a range of possible causes for these symptoms in an older cat including anything from an infectious gastroenteritis, to a kidney issue, an underlying endocrine problem (such as untreated diabetes), or even potentially a toxicity or poisoning.
If your boy is refusing to drink anything at all, then he will quickly become dehydrated, especially if he is continuing to vomit. For this reason alone, you are best to get him seen by your local vet this morning if you can. Here they can carry out a full physical examination as well as a geriatric blood test to check his kidney and internal organ function. Given he hasn't drunk much and is vomiting, they can also start him on some intravenous fluids now as well as given an injection of an antiemetic to stop the vomiting. The blood test may reveal an issue that also needs to be treat straight away. Given his age, I am particularly worried about the progression of a potential kidney issue (such as chronic kidney disease). If this is diagnosed, he may potentially have to stay in the vet hospital for a few days. As he has been on the k/d diet - it sounds like he has been diagnosed with a kidney issue, and in older cats kidney disease continues on and slowly worsens, so it is very likely that this is the case here.
Hopefully you can head down to your local vet clinic now to follow up on his symptoms and to start some treatment for him. It is very likely he will stay in on intravenous fluids, so perhaps take down a comfortable blanket he likes as well. All the best with your boy and let me know how you get on if you get a chance. I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask! If you would like to accept my answer, please press RATE OUR CONVERSATION (I am not compensated in any other way). Bonuses are always welcome. Thanks! I hope to work with you again soon!
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