I have a 15 year old female cat who is a very good cat and has always kept herself well groomed. In the past couple of months, her fur is becoming slightly clumped and is always shedding no matter how much we try to clean the excess fur off. I have also noticed she is not cleaning herself. She has also lately (in the past year) been drinking a ton of water and has taken to haunting the garage and house (she used to be a very active outside cat). Is this just a sign of old age or is there something I can do to get her to start cleaning herself?

Old age is more than likely a factor but if she is drinking more than normal id have her seen by the vet just to make sure she is OK and doesn't have a infection.

Drinking excessive amounts could also indicate diabetes. I would take her to the vet.

It could be diabetes,kidney failure,urinary tract,and even thyroid.Another thing is feline leukemia,only because of hair becoming unhealthy.There is definitley something wrong.If her litter box is full of urine,and I mean soaked,more than likely it's diabetes.Take her to your vet and ask for a general health profile,this should answer all your questions,except for feline leiukemia and FIP.There is a separate test for these diseases.Let us know what you find out.:)