In France, 60,000 patients are receiving renal replacement therapy via dialysis in 2022, 90% of whom are on hemodialysis. This technique is based on the principle of exchange across a membrane between the patient's blood and the dialysate. The goal is to purify the patient's blood as effectively as possible by removing all solutes that have accumulated due to kidney failure. The dialysate is produced from municipal water, which is treated through several processes (reverse osmosis, filtration) to produce ultrapure water. Water consumption at the La Conception Hospital center in Marseille, which conducts 37,000 sessions per year (64 hemodialysis stations), is estimated at 120 m³ of water per day, which is discharged into the sewer system after use. In France, this would correspond to an estimated total consumption of nearly one million m³ of drinking water per year. In the context of climate change, which will lead to a reduction in water resources, it is important to rethink all aspects of water consumption. The investigator's reflection is part of a growing awareness of the environmental impact of dialysis within a working group of the Francophone Society of Nephrology, Dialysis, and Transplantation: "Green Dialysis." The quality of clearance depends on blood flow and dialysate flow rate (Qd). The Qd was set at 500 mL/min based on earlier studies that showed this flow rate corresponded to maximum clearance of urea and the main toxic solutes. These studies were conducted at a time when dialysis membranes were less efficient. Today, the investigators use membranes with higher exchange efficiency. Despite this, the investigators have not reevaluated the appropriateness of a Qd of 500 mL/min. The quality criterion in dialysis is a balanced urea Kt/V measurement >1.2 for a 4-hour session (target set at 1.4 with certain "single-pool" dialysis machine measurement techniques). At the ivnestigator's center, the average urea Kt/V is 1.55 in "single-pool" mode. Reducing the Qd could be done without risk to patients, even if it leads to a decrease in urea Kt/V. A Colombian study with 5 years of follow-up demonstrates patient safety with a Qd of 400 mL/min (vs. 500 mL/min), with no difference in mortality or dialysis efficacy. The study population was not representative of chronic dialysis patients; 10% regained renal function, and the final analysis included only 25 of the 71 patients enrolled.