Increased water intake in dogs

Excessive drinking is a common medical problem in dogs, particularly older ones. This fact sheet discusses how to tell if your dog is really drinking excessively, the causes – common and rare and how the problem can 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. Veterinarians often refer to the combined syndrome as PU/PD.

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A healthy dog may take in between 20 and 70 ml of water per kg of body weight in 24 hours. This figure includes the water in food which obviously varies according to how much dry and how much canned food the dog has. If you notice any increase in the amount of water being drunk by your dog this may be the first indication of a problem and should not be ignored. Dogs on dry diets will need to drink more than dogs on moist food, so if you have recently changed your dog’s diet this may be the reason for a change in drinking habits. If you are worried about how much your dog 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. Try to ensure when you do this that your dog is not drinking water from other sites outside.

If your dog is drinking more, you may notice increased urination. You may notice that your dog is stopping more frequently on a walk to urinate, or you may need to get up in the night to let them out (or come down in the morning to find puddles on the floor). Sometimes an increased urgency in urination caused by diseases of the bladder such as cystitis can be mistaken for increased urination. Dogs with cystitis will usually pass only small volumes of urine, they may be in pain when they urinate and there may be blood staining in the urine. In addition, sometimes urinary incontinence can be mistaken for increased urination and vice versa.

When dogs 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 dog 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 dogs 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:

1. 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.
2. 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 most common causes of excessive drinking are hormonal diseases such as diabetes mellitus and hyperadrenocorticism or cancer or diseases of the kidneys or liver – but all these conditions may show in other ways for example weight loss or changes in appetite and behavior.

There are many other conditions that also have an increase in thirst and urination as part of their clinical signs: high blood calcium levels (hypercalcemia), bacterial infection in the kidneys (pyelonephritis), diabetes insipidus (extremely rare), renal glucosuria, pyometra (infection in the uterus), 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, eg hypercalcemia is often caused by cancers such as lymphoma.

Occasionally excessive thirst is the basic cause, this is called primary polydipsia. It can be due to brain disease or a behavioral abnormality.

A veterinary surgeon will want to ask questions about your dog and examine him. 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 dog will allow your vet to assess if water consumption is excessive. Most dogs 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 dogs 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 dogs are living into old age it is quite common for them to have to cope with more than one condition and combinations of diseases need to be considered.

Finding out the cause of the excessive drinking is the priority so if you think your dog may be drinking more than usual an early visit to your veterinarian is advisable. There will then be options for treatment. Not all options suit every dog or 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.