How do you check a zero water filter?

Remove the cap and place it about an inch into the water by pressing the "on" button. You can see your final reading if you wait for the numbers to be stable. The reading will go back to 000 once you remove theTDS meter from the water.Press the button, remove the lid and place approximately one inch of depth in the water. Wait until the numbers are stabilized and see your final reading. After removing the TDS meter from the water, the reading will return to 1000.