The doppelgänger of the water filter

For years we've had a Brita water system for our drinking water and have changed the filters religiously (that is, we put on a hat).

Michele said this morning that the electronic filter indicator had crapped out and would not flash either green, to show that the filter is working, or red, to show that we need to replace the filter. Without the light, how would we know when to replace the filter? What if we became overchlorinated? What if there was a sudden surge of residual copper or cadmium? The speculations gave me pause. A filter generally lasts two or three months, so Michele changed it today. Then she announced, "I've turned into Jack."