Polyuria is described as urinating too much liquid, and is not to b confused with excessively frequent urination, urinary urgency or dribbling. Urinating too much or too often can indicate several serious conditions.

Causes of polyuria include:
Urinary tract infection (UTI).
Bladder conditions.
Interstitial cystitis.
Type 1 diabetes mellitus.
Type 2 diabetes mellitus.
Gestational diabetes.
Prostate conditions.
Diabetes insipidus.
Congestive heart failure.

For further possible causes of polyuria, please see:
http://www.wrongdiagnosis.com/sym/polyuria.htm