All of you are going to think I'm crazy for asking this question, but how does one know that there is a problem with cats urine. I've had my oldest since July and the youngest since Sept. Both have been to the vet, spayed and all shots given. As far as I know they are in good health. From what I read on this site, URI's and other urinary problems are very common. What should I watch for. They share the same litter box. Thanks for educating me.