Hello, I'm sorry to hear that Snoopy hasn't been herself lately as far as water consumption, urination and litter box accidents. She must be very well taken care of to reach the age of 20. Cats are masters at hiding discomfort or pain so I am not surprised that she is acting as if she isn't in any discomfort.I am glad to hear that her appetite remains very good.Is she losing weight?
An older cat that is drinking more and urinating more is definitely of concern.She may be in kidney failure or diabetic. Or she may have a low grade urinary tract infection or crystals/calculi that are irritating her urinary tract.I highly recommend an examination by her veterinarian, a urinalysis with culture and some blood tests. Although she is an older girl there may be things we can do to keep her healthy and happy longer.
Please let me know if you have any further questions.