Understanding Polydipsia: What illness makes you drink a lot of water?

October 1, 2025 •

4 min read

Excessive and persistent thirst, medically known as polydipsia, is a common symptom of several underlying health issues. While a salty meal or a tough workout can cause temporary thirst, a constant and unquenchable desire to drink is often a sign of more serious conditions, notably what illness makes you drink a lot of water? like diabetes mellitus or diabetes insipidus.

Quick Summary

Excessive, persistent thirst (polydipsia) can signal health problems ranging from diabetes mellitus to diabetes insipidus, kidney disease, or psychological issues. It is often accompanied by increased urination and dry mouth. Consulting a doctor is important for diagnosis and treatment.

Key Points

Polydipsia is a term for excessive thirst: It is a persistent and abnormal feeling of thirst that continues even after drinking ample fluids.
Diabetes mellitus is a primary cause: High blood sugar causes the kidneys to excrete excess fluid and glucose, triggering intense thirst to compensate for the fluid loss.
Diabetes insipidus is distinct from diabetes mellitus: This condition involves a hormonal imbalance or kidney issue that leads to excessive urination and subsequent thirst, not high blood sugar.
Kidney disease can cause constant thirst: When the kidneys fail, their ability to regulate fluid balance and concentrate urine is compromised, leading to increased thirst.
Mental health can be a factor: Psychogenic polydipsia, a compulsive water-drinking behavior, is often linked to psychiatric disorders like schizophrenia and anxiety.
Immediate medical attention is needed for associated symptoms: If excessive thirst is accompanied by frequent urination, weight changes, or blurred vision, consult a doctor to rule out serious conditions.

What is Polydipsia?

Polydipsia is the medical term for excessive, persistent thirst that is difficult to quench, even after drinking a significant amount of fluid. It is frequently linked with another condition called polyuria, which is the passage of an unusually large volume of urine. These two symptoms often occur together and are key indicators of a problem with the body's fluid regulation system. While normal thirst is the body's way of signalling the need for hydration, polydipsia indicates an underlying issue where this thirst-sensing mechanism is malfunctioning or working in overdrive to compensate for fluid loss.

Medical Conditions Causing Excessive Thirst

Diabetes Mellitus (Types 1 and 2)

One of the most well-known causes of constant thirst is diabetes mellitus. This condition prevents the body from effectively using glucose (sugar) for energy.

The mechanism: High blood sugar (hyperglycemia) forces the kidneys to work harder to filter and absorb the excess glucose. When they can't keep up, the kidneys excrete the extra sugar into the urine, pulling fluids from the body's tissues along with it. This leads to increased urination (polyuria) and dehydration, which triggers intense thirst.
Associated symptoms: In addition to excessive thirst and urination, symptoms include fatigue, unexplained weight loss, blurry vision, and slow-healing sores.

Diabetes Insipidus

Despite the similar name, diabetes insipidus (DI) is a different condition from diabetes mellitus and does not involve high blood sugar levels. It is a rare disorder that occurs when the kidneys are unable to conserve water.

Central DI: This type is caused by a problem with the hypothalamus or pituitary gland, which are responsible for producing and storing the antidiuretic hormone (ADH). A lack of ADH means the kidneys release too much water, leading to excessive urination and subsequent thirst.
Nephrogenic DI: In this case, the pituitary gland produces enough ADH, but the kidneys do not respond to it correctly. This can be caused by genetic issues, medications (like lithium), or chronic kidney disease.
Gestational DI: A rare form that can occur during pregnancy when an enzyme produced by the placenta destroys ADH.
Associated symptoms: Adults may urinate up to 20 quarts a day, far exceeding the normal 1 to 3 quarts, leading to a constant desire for cold water.

Chronic Kidney Disease

As kidney function declines, the body's ability to balance fluids and electrolytes is impaired.

The mechanism: Failing kidneys may not be able to concentrate urine properly, forcing them to excrete more water to get rid of dietary solutes. This fluid loss drives the sensation of thirst to prompt the individual to drink more water.
Associated symptoms: Excessive thirst is a key symptom of advanced kidney disease, along with fatigue, shortness of breath, swelling in the hands and feet, and problems concentrating.

Psychogenic Polydipsia

This is a compulsive behavioral condition where a person drinks excessive amounts of water in the absence of a physiological need.

The mechanism: It is often linked to underlying mental health disorders such as schizophrenia, bipolar disorder, or anxiety. The overconsumption of water can lead to a dangerous dilution of sodium in the blood (hyponatremia), which can cause serious neurological symptoms.
Associated symptoms: Compulsive water-seeking behavior, headache, confusion, seizures, and other effects of low blood sodium levels.

Dehydration

While often a temporary state, severe or prolonged dehydration can cause constant, intense thirst.

The mechanism: Dehydration occurs when the body loses more fluid than it takes in, whether from heavy sweating, vomiting, or diarrhea. This fluid loss triggers the brain's thirst centers to encourage rehydration.
Associated symptoms: Mild dehydration includes dry mouth, headache, and dizziness. Severe dehydration can lead to more critical symptoms like fatigue, low blood pressure, and fainting.

Comparison of Major Causes of Polydipsia


Feature	Diabetes Mellitus	Diabetes Insipidus	Psychogenic Polydipsia
Underlying Problem	High blood sugar (hyperglycemia) due to insulin issues.	Problem with ADH hormone or kidney response to ADH.	Compulsive water-drinking behavior, often linked to mental illness.
Mechanism of Thirst	Kidneys excrete excess glucose and fluids, causing dehydration.	Kidneys excrete excessive, dilute urine, leading to fluid loss.	Primary urge to drink, leading to overhydration and potential electrolyte imbalance.
Blood Sugar Levels	High.	Normal.	Normal.
Urine Volume	Excessive (polyuria), pulling water with glucose.	Excessive and very dilute.	Excessive, very dilute urine due to high fluid intake.
Key Laboratory Test	Blood glucose/A1C test.	Water deprivation test or copeptin test.	Diagnosis of exclusion, often requires psychiatric evaluation.

Conclusion

While a variety of conditions, both common and rare, can cause a person to drink a lot of water, the underlying reasons are complex and should not be self-diagnosed. The most prominent causes are related to how the body handles glucose (diabetes mellitus) or how it manages water balance through hormones and kidneys (diabetes insipidus, chronic kidney disease). In some cases, a psychological or compulsive component can be the driver. Ignoring persistent excessive thirst can lead to serious complications such as severe dehydration or dangerously low blood sodium levels. If you experience this symptom, especially when accompanied by other signs like frequent urination, unexplained weight loss, or fatigue, it is crucial to consult a healthcare professional for proper evaluation and diagnosis. The right treatment depends entirely on identifying the correct underlying cause, and early intervention can prevent more severe health issues.

For more information on these topics, consult authoritative resources such as the National Institutes of Health (NIH).

Frequently Asked Questions

The medical term for excessive, persistent thirst that leads to drinking too much water is polydipsia. It can be a symptom of several medical conditions, most notably diabetes mellitus and diabetes insipidus.

Yes, increased thirst can be a normal reaction to certain activities or foods, such as eating salty or spicy foods, exercising, sweating heavily in hot weather, or having a fever. However, if the thirst is constant and unexplained, it should be evaluated by a doctor.

Despite their similar names, diabetes insipidus is different from diabetes mellitus. Diabetes insipidus is a rare disorder related to a hormone that regulates water in the body, while diabetes mellitus is a common condition related to high blood sugar levels (glucose).

Yes, certain medications can have excessive thirst as a side effect. Examples include lithium, diuretics (water pills), and some types of antidepressants and antipsychotics.

Psychogenic polydipsia is a compulsive psychological condition where a person drinks excessive amounts of water, not because of a physiological need, but often due to an underlying mental health disorder.

You should see a doctor if your excessive thirst is unexplained, persists for several days, or is accompanied by other symptoms like frequent urination, fatigue, blurry vision, or unexplained weight loss.

No, drinking plenty of water is generally healthy, but the 'excessive' and 'persistent' nature of polydipsia is the key differentiator. If your thirst is constant and doesn't go away, it warrants medical investigation.