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Increased water intake in cats

Drinking more is a common medical problem in cats, particularly older cats. This factsheet discusses how to tell if your cat is really drinking excessively, the causes - common and rare and how the issue may be managed. The medical term for an increased thirst is polydipsia and for an increase in the volume of urine being produced it is polyuria. Vets often refer to the joint syndrome as PU/PD.

Your questions answered

What is normal water intake?

A healthy cat may take in between 20 and 90 ml of water per kg of body weight per 24 hours. This figure includes the water in food which obviously varies according to how much dry and how much canned/pouched food the cat has. So it is not until your cat is drinking around 100 ml of water per kg body weight (for an average cat this is around 300-400ml) per day that you can be sure this is excessive.  However, most cats do not drink this much and for many a lesser intake may be significantly abnormal so if you notice any increase in the amount of water being drunk by your cat this may be the first indication of a problem and should not be ignored. Cats on dry diets will need to drink more than cats on moist food so if you have recently changed your cat's diet this may be the reason for a change in drinking habits. If you are worried about how much your cat is drinking you might want to try to measure their actual intake.  The easiest way to do this is fill their bowl with a known volume of water using a jug and then at the end of the day measuring how much water is left. Of course, for many cats, this is difficult as they drink outside, from sources other than their bowl and often share a water bowl with other animals. To measure the water intake in these cats you might have to isolate your cat and keep her indoors for three days.

If your cat is drinking more you may notice increased urination. Here we are most interested in an increase of the total volume of urine being produced. Again, this may not be noticed in cats that are outside for much of the day but, for other cats, owners may notice that the litter needs changing more often or that litter training is lost. If your cat is visiting the litter tray more often this may not be due to an increase in urine volume. Often it will be due to increased urgency in urination caused by diseases of the bladder such as cystitis. These cats will usually pass only small volumes of urine, they may vocalise as they are irritated or in pain and there may be blood staining.

Why might my cat be drinking more?

When cats are drinking more it is nearly always caused by a disease (either based in the kidneys or elsewhere in the body but affecting the kidneys secondarily) that is causing the kidneys to make dilute urine and the cat then has to drink to stop being thirsty. So it is actually usually the increased urine production that happens first and the increased drinking is to compensate. In the vast majority of cats that are drinking excessively it is because they are genuinely thirsty as their kidneys are making more urine, their bodies are detecting the loss of fluid and stimulate the desire to drink. There are two main reasons for this: either there is a problem with a hormone that regulates the concentration of urine - this is best known as ADH (anti-diuretic hormone). It may be that there is not enough ADH being produced or it may be that the kidneys fail to react to the ADH. The second cause is that the urine contains large amounts of an abnormal substance that draws water out with it into the urine by a physical process called osmosis; an example is glucose (sugar) in the urine of a diabetic.

The commonest diseases that often show up as a cat drinking excessively are chronic kidney failure, diabetes mellitus and hyperthyroidism - but all these conditions may show in other ways for example weight loss or changes in appetite and behaviour.

There are many other conditions that also have an increase in thirst and urination as part of their clinical signs: high blood calcium levels (hypercalcaemia), low blood potassium (hypokalaemia), bacterial infection in the kidneys (pyelonephritis), liver failure, acromegaly and hyperadrenocorticism (each of which show with signs of diabetes mellitus), acute renal failure (especially in the recovery phase), diabetes insipidus, renal glucosuria; pyometra (infection in the uterus), hypoadrenocorticism and damage to the pituitary gland. Other possibilities that should be obvious but must be considered are certain drugs such as the diuretics often used to treat heart failure and some foods that are designed to promote water intake by being high in salt.

There are also important underlying diseases that must be considered. For example hypercalcaemia is often caused by cancers such as lymphoma and hypokalaemia might be caused by hyperaldosteronism (Conn's syndrome).

Occasionally excessive thirst is the basic cause, this is called primary polydipsia. It can be due to brain disease or a behavioural abnormality. In cats the commonest cause of primary polydipsia is probably as part of the common endocrine condition hyperthyroidism.

How can the cause of the increased thirst be found?

A veterinary surgeon will want to ask questions about your cat and examine her. Most of the causes of PU/PD will give other clues that they are present. If there is uncertainty about the extent of the problem then actually measuring the volume of water drunk (daily for about three days) and weighing your cat will allow your vet to assess if water consumption is excessive. Most cats will require a combination of blood and urine tests as an initial investigation and the common causes of PU/PD are usually easily diagnosed or ruled out. Some cats will require a more in-depth investigation to uncover their problem involving further blood tests, imaging with ultrasound or x-rays and the taking of biopsies.

One important point is that now many cats are living into old age it is quite common for them to have to cope with more than one condition and combinations such as chronic renal failure and hyperthyroidism need to be considered.

What can be done to help my cat?

Finding out the cause of the excessive drinking is the priority so if your think your cat may be drinking more than usual an early visit to your vet is advisable. There will then be options for treatment. Not all options suit every cat and each owner but the conditions listed above can all be helped, to varying degrees. One thing that is common to all is that in no circumstances should water be withheld.

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