cat & peeing

Question
Lily, 2 yrs old, spayed female.  I have taken her to vet and ruled out UTI.  She uses the litter box but every 3 or 4 days she will pee on the carpet.  I have changed litter, bought new boxes, added boxes, moved boxes around.  Lily is on prozac and right now since we just put in new carpet she is confined to the spare bedroom.  My question is... how long can a cat hold their pee?  She last went pee yesterday morning around 9 am it is now 6 pm the next day thats approx. 20 hrs!!!  Also, the UTI was ruled out but could there be another physical problem with her that would make urination painful.  She doesn't act like she's in pain and when she's in the box she is not straining.  Thanks

Answer
Hi Christine!
I really do not know for sure, but that does seem like a long time.  I guess it really depends on her fluid intake.  I would watch her closely and see if this continues.  It may be her new meds.  As long as you don't see blood in the urine, and/or straining, then she is probably ok.  Keep a close eye and make sure she drinks plenty of water.
God Bless,
Becky