DIAGNOSIS On pitchers with the electronic Smart Light, the battery is likely dead, or the button contacts are stuck or dirty. The light is on a simple timer and doesn't actually test the water.
FIX First, try a hard reset. 1) Remove the filter and the battery cover (usually on the handle). 2) Take out the old coin-cell battery (typically a CR2032). 3) Press and hold the reset button for 30 seconds with the battery out. 4) Insert a fresh, name-brand battery, positive side (+) facing out as shown. 5) Reinstall the filter and press the reset button once. The light should cycle to green.
IF THAT DIDN'T WORK Check for corrosion on the battery contacts inside the compartment. If you see white or blue crust, gently clean it with a cotton swab dipped in vinegar or rubbing alcohol. Let it dry completely before inserting the new battery.
HEADS UP The indicator is just a timer. It doesn't know your water quality or usage. If you have hard water, you might need to change filters before the light turns red. Always go by taste and flow rate, not just the light.