Similar story here. I would guess an ultrasonic sensor would be the most reliable solution for OP, since all the tech can be kept at the top of the well. The only minor question I have is whether echoes would be an issue in a well, but I think it's worth trying to find out! You can get inexpensive preassembled units that work with Zigbee/Tuya,

Edit: This is what I used as a cheap off-the-shelf solution - https://a.aliexpress.com/_mPR6XlJ