From our discussion it seems that your cat may be drinking more than it should or more than it usually does.

Drinking more is a common medical problem in cats, particularly in older cat.

Drinking excessively is known as polydipsia, passing increased amounts of urine is called polyuria, obviously these two things often go together and vets will often talk about this as PUPD.

Excessive drinking is defined as a cat drinking more than 100ml of water per KG of body weight but this can be hard to measure if cats go outside and may drink elsewhere and it will depend on how much fluid they take with their food. Cats eating dry food will often appear to drink more than cats on wet food.

The three most common causes of excessive thirst are Chronic kidney failure, diabetes and an overactive thyroid gland which is known as hyperthyroidism. Although there are also other causes that are less common.

The most important thing to know is that increased thirst without any change of diet does usually indicate that there is a medical problem and any increase in drinking beyond what you would normally expect should be looked into by your vet.

You may only notice that the litter tray needs changing more often if the cat can drink where you don’t see it.

Blood and urine samples will often be required to discover the cause of the excessive thirst and this is best done as soon as possible during normal opening hours as many conditions that cause excessive urination and drinking are progressive and will become more serious if neglected.

If you can collect a urine sample to take to the clinic when you visit this can be a great help in speeding up the investigation. This is not always easy but you can obtain non-absorbent litter or just put tissue in the tray and wring a small amount of urine into a clean container. A small sample can tell your vet a lot so don't worry about getting a big sample.

Older pets may often be dealing with multiple issues for instance kidney disease and hyperthyroidism at the same time so a careful investigation by your vet will be necessary to make sure your pet gets the best treatment.

I recommend that you contact your vet during normal working hours so this can be investigated.