Many people have asked about a sensor input option like a water level sensor. The question is what’s the specific logic to follow when the sensor is triggered. For example, in your specific case, if the tank does not have enough water, do you want to postpone the watering, or just cancel the watering? You can actually utilize the rain sensor and use a water level sensor as if it’s a rain sensor. The rain sensor logic is that if the sensor is activated, it simply stops watering. Currently the firmware does not support postponing any watering schedule.