SYMPTOM
Increased thirst
Drinking noticeably more water than usual, which may be gradual or sudden depending on the underlying cause.
Renal
The kidneys play a central role in water balance, and conditions affecting their concentrating ability can produce increased thirst as a compensatory mechanism. Chronic kidney disease progressively impairs the kidneys' ability to concentrate urine, leading to increased water loss and a compensatory increase in drinking. In chronic kidney disease the polydipsia develops gradually and is usually not evident until around two-thirds of the nephrons have been lost. Acute kidney injury is different: toxins such as lilies in cats, grapes or raisins and ibuprofen, and some kidney infections, damage the kidneys over hours to days, and any increase in drinking may come with vomiting, lethargy, poor appetite and reduced or absent urine.
Endocrine
Several hormonal conditions directly influence water balance and thirst. Diabetes mellitus produces osmotic diuresis through glucosuria, driving increased water intake to compensate for urinary losses. Hyperadrenocorticism affects the kidney's response to antidiuretic hormone, producing polydipsia alongside polyuria. Hyperthyroidism increases metabolic rate and renal blood flow, indirectly increasing water turnover. Diabetes insipidus, whether central or nephrogenic, directly impairs the body's ability to conserve water, producing marked polydipsia.
Hepatic
Severe liver disease or a portosystemic shunt reduces the liver's production of urea, which the kidneys need in order to concentrate urine, so more dilute urine is passed and drinking rises. Animals with significant liver dysfunction may show increased thirst alongside other signs such as altered appetite, gastrointestinal changes, and in some cases visible jaundice or ascites.
Infection or Inflammation
Systemic infections, particularly pyometra in intact females, can produce marked polydipsia through the release of bacterial toxins that interfere with the kidney's concentrating ability. Other infections producing fever and increased metabolic demand may also increase water requirements. Kidney infections such as pyelonephritis and leptospirosis can also reduce the kidneys' concentrating ability.
Medication-Related
Several commonly used medications can increase thirst as a predictable side effect. Corticosteroids, whether administered orally, by injection, or topically in sufficient doses, frequently produce polydipsia alongside polyphagia and polyuria. Certain diuretics, anticonvulsant medications, and other drugs may similarly affect water balance. The increased thirst usually settles once the dose is reduced or the course ends. Long-term corticosteroid treatment is not stopped abruptly, because sudden withdrawal can bring on signs of adrenal insufficiency (hypoadrenocorticism).
Behavioural or Psychogenic
Some animals develop patterns of excessive water consumption that are not driven by a physiological need for increased fluid intake. Psychogenic polydipsia, while less common than medical causes, can occur in animals experiencing boredom, anxiety, or attention-seeking behaviour. This diagnosis is typically considered only after medical causes have been explored, as the vast majority of polydipsia in companion animals has an identifiable physiological basis.
Why timing matters
Early observation
Early increases in thirst may be subtle and easily attributed to environmental factors such as warm weather, increased activity, dietary changes, or the normal day-to-day variation in drinking. The animal may begin visiting the water bowl more frequently, drinking larger amounts at each visit, or seeking water from unusual sources such as taps, toilets, or puddles. At this stage, quantifying water intake can help establish whether a genuine increase has occurred, as subjective assessment of "drinking more" can be unreliable. In dogs, daily water intake above about 90 to 100 ml per kilogram of body weight is generally considered increased, and in cats intake above about 45 ml per kilogram per day.
Later presentation
As polydipsia progresses, the increase in water consumption typically becomes unmistakable. The animal may empty water bowls repeatedly, drink greedily or for prolonged periods, and show obvious distress if water is not readily available. The increased water intake is almost always accompanied by increased urine output, which may itself create secondary problems such as house-soiling, need for more frequent outdoor access, or overflow of litter boxes. At this stage, the body's fluid balance mechanisms are clearly stressed, and dehydration may occur rapidly if water access is restricted.
The trajectory of increased thirst mirrors the course of its underlying cause. Polydipsia from chronic kidney disease tends to progress gradually over months to years as nephron loss accumulates, whereas acute kidney injury develops over hours to days. Endocrine causes may progress at variable rates depending on the specific condition. Infection-related polydipsia may develop acutely and resolve with treatment of the underlying infection. Medication-related polydipsia typically remains stable while the medication continues. Understanding whether the thirst increase has been gradual, sudden, progressive, or stable helps contextualise the type of process involved.
Conditions commonly associated
Chronic Kidney Disease in Cats
In chronic kidney disease, damaged nephrons lose the ability to concentrate urine, so cats pass larger volumes of dilute urine and drink more to replace the fluid lost.
Chronic Kidney Disease in Dogs
As kidney function declines, the kidneys can no longer concentrate urine effectively, so dogs lose more fluid through urination and compensate by drinking more.
Diabetes Mellitus in Dogs
Persistently high blood glucose exceeds the kidneys' capacity to reabsorb it, drawing water into the urine by osmosis and prompting dogs to drink more to offset the fluid loss.
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Diabetes Mellitus in Cats
When blood glucose remains elevated, excess sugar spills into the urine and pulls water with it, increasing fluid loss and driving cats to drink more.
Hyperthyroidism in Cats
Excess thyroid hormone raises metabolic rate and blood flow through the kidneys, increasing urine output and prompting a corresponding rise in water intake.
Cushings Disease in Dogs
Elevated cortisol interferes with the kidneys' response to antidiuretic hormone, reducing their ability to concentrate urine and leading dogs to drink more to compensate for the increased fluid loss.
Pyometra
Toxins released by the bacteria reduce the kidneys' ability to retain fluid, so more urine is produced and drinking rises; pyometra is a life-threatening infection.
Portosystemic Shunt
With blood bypassing the liver, less urea is made, which reduces the kidneys' ability to concentrate urine, so more dilute urine is passed and drinking increases.
Adrenal Tumours
A cortisol-secreting adrenal tumour drives excessive drinking as one of its most consistent effects.
Adrenocortical Carcinoma
A functional adrenocortical carcinoma secreting cortisol drives noticeably increased drinking.
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Cushings Disease in Cats
Most cats with this condition also have diabetes mellitus, often poorly controlled, and the high blood glucose that results drives increased urination and a noticeable rise in thirst.
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Renal Lymphoma in Cats
Lymphoma infiltrating the kidneys reduces their ability to concentrate urine, driving a compensatory rise in drinking.
Atypical Cushings in Dogs
Excess adrenal hormone activity affects how the kidneys concentrate urine, driving thirst upward.
Diabetes Insipidus
An inability to concentrate urine means far more water is lost, driving the body to drink heavily to keep pace.
Grape and Raisin Toxicity in Dogs
Vomiting or diarrhoea usually starts within 6 to 12 hours of eating grapes or raisins, and kidney failure with little or no urine can develop within 24 to 72 hours; increased drinking may be seen as the kidneys are damaged.
Hyperaldosteronism in Cats
Increased thirst can develop as the excess hormone drives the kidneys to retain sodium and lose potassium.
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Ibuprofen Toxicity
Stomach and gut irritation are the most commonly reported effects, and higher doses can cause kidney failure, in which increased thirst may be seen. Cats are affected at about half the dose that harms dogs.
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Leishmaniasis
Increased drinking can develop where the infection affects the kidneys, a well-recognised complication of this disease.
Lily Toxicity in Cats
Vomiting, drooling and lethargy begin within 1 to 3 hours of exposure, and increased urination follows over the next 12 to 30 hours as the kidneys are damaged; the outlook is excellent when treatment starts early and guarded to poor once urine output falls.
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Polycystic Kidney Disease in Cats
Cysts gradually replacing healthy kidney tissue reduce the kidneys' ability to concentrate urine, so affected cats drink more to compensate for the extra fluid lost.
Pyelonephritis
An actively infected, inflamed kidney loses some of its ability to concentrate urine, so affected pets drink more to compensate for the extra fluid lost.
Steroid Hepatopathy
The excess steroid that causes this liver change also interferes with the kidneys' response to antidiuretic hormone, which drives a noticeable rise in water intake.
Sudden Acquired Retinal Degeneration Syndrome (SARDS)
This condition often develops alongside a Cushing's-like hormonal picture, so increased water intake is frequently noticed around the same time as the vision loss.
Acute Kidney Injury
Sudden kidney damage from toxins such as lilies, grapes or raisins and NSAIDs, or from infections such as leptospirosis, can cause increased urination and thirst, although some animals instead produce little or no urine.
Diabetic Ketoacidosis
A life-threatening complication of uncontrolled diabetes, in which the increased thirst of diabetes is joined by vomiting, poor appetite and dehydration.
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Leptospirosis
Acute kidney injury is the most common presentation in dogs, and some dogs drink and urinate more even while blood kidney values are still normal.
When to explore further
When increased thirst is accompanied by increased urination and increased appetite, this triad of polydipsia, polyuria, and polyphagia may suggest an endocrine or metabolic condition that is affecting multiple physiological systems simultaneously, and the presence of all three signs together is a recognised pattern associated with specific conditions.
A sudden and dramatic increase in water consumption in a previously normal animal may suggest an acute process. In an unspayed female, pyometra (infection of the womb) is a leading concern: in bitches it usually develops four to six weeks after a season (reported range two to sixteen weeks), bacterial toxins reduce the kidneys' ability to retain fluid, and the thirst often comes with lethargy, poor appetite, vomiting or a vaginal discharge. When the cervix is closed there is no discharge, the abdomen may swell and affected dogs become severely ill very quickly; untreated, the infection is fatal in many cases.
Increased thirst developing alongside weight loss, despite maintained or increased food intake, may suggest a condition where the body's metabolism is accelerated or where nutrients are not being effectively utilised, creating a metabolic imbalance that drives both thirst and wasting.
When polydipsia is accompanied by changes in urine appearance (notably very pale, almost water-like urine in large volumes), the combination suggests that the kidneys are producing dilute urine either because they cannot concentrate it or because they are being overwhelmed by excess water intake.
Increased thirst that develops in a middle-aged or older animal alongside subtle changes such as lethargy, coat quality decline, or muscle wasting may represent the early manifestation of a progressive condition, and the gradual nature of the onset should not diminish the significance of the pattern.
Measuring actual water intake over several days can provide objective data that is more reliable than subjective impressions. Using a measured volume of water and recording how much is consumed over a 24-hour period, repeated over several days, establishes a quantitative baseline. Noting whether the increased thirst follows any pattern (varying with activity, temperature or time of day) and whether it is accompanied by proportional increases in urination adds context. Observing the urine itself, including its colour, volume per void, and frequency, provides complementary information about how the body is handling the increased fluid intake. Several days of measuring suits a pet that is otherwise bright and eating normally. It does not fit thirst that comes with vomiting, lethargy, poor appetite, or reduced or absent urine, thirst in an unspayed female in the weeks after a season, or thirst after any possible contact with lilies (cats), grapes or raisins, or ibuprofen. In those situations the causes include pyometra, acute kidney injury and diabetic ketoacidosis, which can become life-threatening within hours to days and cannot be judged at home.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS