Patients affected by Autosomal Dominant Polycystic Kidney Disease (ADPKD) need a safe and effective long-term treatment regimen. Unfortunately, there are still no disease-specific treatment for ADPKD approved in the US. A rational step towards identifying such agents is to test therapies that have a proven safety profile with mechanisms of action that can counter the disease progression.

The purpose of this study is to investigate whether drinking increased amounts of water (water loading) might slow down polycystic kidney growth or kidney function decline. Water loading can cause the suppression of a pathway that causes fluid buildup and cyst growth. High water intake has been safely used in the clinical setting, such as in the case of kidney stone therapy. New York State tap water is widely available and safe, making it highly cost-effective as well.

The study will involve 11 visits to the study site over 19 months. Participants will need to follow specific dietary and fluid recommendations. There will be physical examinations and medical history assessments at each visit. Testing will include undergoing magnetic resonance imaging (MRI), blood and urine tests. Study participants will be compensated for their time. Detailed study procedures will be reviewed upon contact with the study team.

Inclusion Criteria:

• pre-existing diagnosis of Autosomal Dominant Polycystic Kidney Disease
• estimated glomerular filtration rate of 40 ml/min or greater
• urine osmolality > 400 mOsm/L

Exclusion Criteria:

• estimated glomerular filtration rate less than 40 ml/min
• low blood sodium levels
• syndrome of inappropriate diuretic hormone
• use of thiazide diuretics or selective serotonin reuptake inhibitors (SSRIs)
• use of tolvaptan, another vasopressin receptor antagonist, vasopressin agonists or dDAVP
• contraindications to magnetic resonance imaging (MRI) (pacemakers, defibrillators, implanted electronic devices, metallic foreign body)

The radiologist measuring kidney volumes will be masked to the study condition.