Filters should be changed every 200 or so liters [about 70 gallons] depending on the quality of your source water. It is suggested to test the pH periodically to ensure the filter is still ionizing. Alkaline Water Plus is conducting a long-term test on the WellBlue filter and we’ve filtered over 40 gallons so far with no drop in pH or ORP. We have discovered that it takes 15-30 minutes to filter if you fill the upper bin completely, and that you should wait at least one hour between filterings to ensure your pH and ORP will not drop off [due to overuse of the filter]. If you want to filter more water than that we suggest you purchase another filter