[header] How to know if your cat has kidney issues [title] Monitor your cat's drinking habits. [step] Check the level of your cat's water bowl at the start of each day. See if your cat has started to drink more water on a daily basis. 
You can also tell if your cat's water intake has increased by watching to see if you are cleaning out more wet litter than normal. Most cats are very efficient at processing water and don't require very much of it, so increased urinating and drinking can be a sign of kidney problems.