Cat not eating, lethargic

Question
My 10 year calico female is not eating today.  She is very lethargic and is drinking more water than usual.  She doesn't appear to be in any pain. All her shots are current, as are her sister's, and both are indoor cats.  She will cry when picked up ... but I think that's only to tell me that she's not feeling well ... other than that she's quiet.  

Answer
Hi Sidney!  I would recommend taking her to your veterinarian promptly.  Anytime a cat refuses food, is lethargic, and/or has increased water intake, this indicates fever, dehydration, and illness.  Is she using the litter box okay?  The list of possibilities is broad, at this point.  This could be caused by a bladder infection,a urinary tract infection, respiratory infection, an intestinal infection, or many other things, including (if she is not spayed) a Pyometra, which is a severe and potentially deadly uteran infection.  Blood work and a physical examination will be needed for diagnosis and treatment.  In the meantime, you may want to pick up some baby food (chicken/beef), as this will sometimes stimulate appetite.  You may also want to take her temperature rectally with a digital thermometer.  101.5-102.5 is the normal range of temperature for a cat.  If her temperature is above 103, applying rubbing alcohol to her paw pads will decrease her fever.  Getting her into your veterinarian first thing tomorrow would be very important.
Please let me know how she does and best of luck,
Hilary