This trial is testing if adding hydrochlorothiazide, a common blood pressure medication, to the existing kidney disease treatment Tolvaptan can improve its effectiveness and reduce side effects. The study targets adults with a specific type of kidney disease who are already on Tolvaptan. Tolvaptan helps slow kidney damage but can cause excessive urination, and hydrochlorothiazide might help manage this issue. Tolvaptan is the only approved drug for this type of kidney disease and has been shown to slow its progression.