This study aims to better understand electrolyte handling in patients with autosomal dominant polycystic kidney disease treated with the SGLT2 inhibitor Empagliflozin. Patients will be randomized into two groups and take Empagliflozin or a Placebo for 2 weeks with a wash-out period of 2 weeks. The primary outcome is tubular handling of the divalent ions calcium, phosphate and magnesium. Secondary outcomes include diuresis, safety and tolerability.