Diabetes Mellitus: This is the most common cause of polyuria and polydipsia, resulting from insufficient insulin production or insulin resistance, leading to high blood glucose levels that exceed the renal threshold, causing glucose to spill into the urine and resulting in osmotic diuresis.

Diabetes Insipidus (Central or Nephrogenic): Characterized by the inability to regulate fluids in the body due to problems with the antidiuretic hormone (ADH), leading to excessive thirst and urination.
Primary Polydipsia: Also known as psychogenic polydipsia, this condition involves excessive water drinking due to psychological factors, leading to polyuria as the body tries to eliminate the excess water.
Hypercalcemia: Elevated calcium levels can affect the kidneys' ability to concentrate urine, leading to polyuria.
Hypokalemia: Low potassium levels can impair the kidneys' concentrating ability, resulting in polyuria.

Diabetic Ketoacidosis: A serious complication of diabetes that can present with polyuria and polydipsia, along with other symptoms like nausea, vomiting, and abdominal pain. It requires immediate medical attention.
Hyperosmolar Hyperglycemic State: A life-threatening condition that occurs in patients with diabetes, characterized by very high blood glucose levels, polyuria, polydipsia, and altered mental status.

Nephrogenic Diabetes Insipidus due to Genetic Mutations: Rare genetic disorders affecting the kidneys' response to ADH, leading to polyuria and polydipsia.
Sjögren's Syndrome: An autoimmune disorder that can cause renal tubular acidosis, leading to polyuria.
Barter Syndrome: A rare genetic disorder affecting the kidneys' ability to absorb potassium, leading to polyuria and other electrolyte imbalances.
Liddle Syndrome: A rare genetic disorder characterized by excessive sodium absorption in the kidneys, leading to hypertension and polyuria.