How much water is used during the Reverse Osmosis process? January 28, 2026 22:21 Updated 1 Gallon : 5 GallonsFor every gallon of RO water produced, the system will drain five gallons of water on average. Related articles Constant Draining on Reverse Osmosis How Does A Reverse Osmosis System Work? How to Purge Your Reverse Osmosis System WHAROS5 Manual WHES40 / WHES44 Manual