What can cause Urine Potassium loss due to high volume and excessive urination?

What medical conditions could cause an onset of polyuria (excessive urination) with high concentrations of potassium in the urine beginning at around age 7 and continuing into adulthood currently 32 year old male, 6 liters of urine output in 24 hours with 124 meq of potassium in the same volume. also having symptoms of dehydration and lab tests showing mild serum hypokalemia 3.0 to 3.4.... Hyperglycemia has been ruled out.