For your peace of mind, have a urinalysis done. Get a urine sample from Popsie (you'll need a sterile, or at least a very clean container), and refrigerate it until you can get it to the vet. They'll be able to see if Popsie is concentrating his urine (a good thing).
I noticed the same thing in one of my babies that you've been observing with Popsie. I got the urine sample (way easier than I though it would be!) and the next day got the good news that it was fine. I'd also recently done bloodwork for my cat, which is another important way to determine kidney function. Her levels were normal, but high normal, so we did the urinalysis too.
Since you don't have to take Popsie in to the vet to have the urinalysis done (unless you really can't get a sample) start with that. With kidney disease, the sooner you start treatment, the better. Hopefully, that's not why Popsie's drinking more water.