Autosomal dominant polycystic kidney disease (ADPKD) is the most common single gene disorder that is potentially fatal. ADPKD is caused by mutations in either of two genes (PKD1, PKD2). Cysts begin to develop primarily in renal collecting tubules in utero and continue to form and expand throughout the patient's life. One of the goals of the study is to formulate a water prescription for use in clinical trials to determine the effect of sustained water diuresis on the progression of ADPKD.