The easiest way to tell is if you see foaming in your cooling tower. You may also see bits of the electrolyser byproduct stuck to the inside of the cooling tower after the foam has dissipated. The foam can reach the tube leading out of the tower and travel into the humidifier. From there, it can cause overflow into the drinking water bubbler.
If you see signs of contamination, drain and discard your lye solution and the water from the humidifier and drinking water bubbler. Rinse your AquaCure, tower, tubes, and bottles and start with a fresh batch of lye solution.