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. The polydipsia in renal disease tends to develop gradually as kidney function declines, and the animal may initially show only modest increases in water intake that become more pronounced over time.
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
Liver disease can affect water balance through multiple mechanisms, including altered metabolism of hormones that regulate water balance, changes in blood protein levels that affect fluid distribution, and the accumulation of metabolic waste products that stimulate thirst. 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. Inflammatory conditions affecting various organ systems can produce cytokines and other mediators that influence thirst centres and renal water handling.
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 typically develops within days of starting the medication and resolves when the medication is discontinued.
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 — warm weather, increased activity, dietary changes, or the normal variation in drinking that occurs day to day. 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. For dogs, daily water intake exceeding approximately 100ml per kilogram of body weight is generally considered increased.
Later presentation
As polydipsia progresses, the increase in water consumption typically becomes unmistakable. The animal may empty water bowls repeatedly, drink urgently 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. Kidney disease-related polydipsia tends to progress gradually over months to years as nephron loss accumulates. 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.
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
Pyometra often causes increased thirst as bacterial toxins affect kidney function and the body attempts to flush out toxins.
Portosystemic Shunt
Altered kidney function and reduced urine concentrating ability in portosystemic shunt cases causes polydipsia.
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.
Cushings Disease in Cats
Excess cortisol produced in this condition increases urine output, which in turn drives a noticeable rise in thirst.
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
Early kidney injury from the toxin can disrupt the kidneys' ability to concentrate urine, driving noticeably increased drinking.
Hyperaldosteronism in Cats
Increased thirst can develop as the excess hormone drives the kidneys to retain sodium and lose potassium.
Ibuprofen Toxicity
The drug can reduce blood flow through the kidneys, and the resulting kidney injury often first shows up as a noticeable rise in thirst.
Leishmaniasis
Increased drinking can develop where the infection affects the kidneys, a well-recognised complication of this disease.
Lily Toxicity in Cats
Thirst can increase in the early stages as the damaged kidneys lose their ability to concentrate urine.
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
Excess circulating steroid affecting the liver and kidneys 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.
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, particularly in an intact female, may suggest an acute process such as uterine infection, which can produce rapid changes in water balance through the effects of bacterial toxins on kidney function.
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.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS