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
Chronic Kidney Disease in Dogs
Diabetes Mellitus in Dogs
Diabetes Mellitus in Cats
Hyperthyroidism in Cats
Cushings Disease in Dogs
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.
Polycystic kidney disease often leads to increased water consumption as kidney concentrating ability declines.
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