Here is a tested Arduino project that uses 3 sensor probes as water level indicator with 3 leds and one LCD display + a simple controller that turns on a motor when the water has reached the desired ...

I was thinking there must be a simple sensor that could tell me when the water level has fallen a set amount and automatically run the "fill pool" zone on the Rachio.

Now with a new ultrasonic sensor developed by Centre for Development of Advanced Computing (C-DAC), the KWA is getting updates about water level at regular intervals via SMSs.