I've been playing around with a couple of ESP32 microcontrollers, and that experimentation has taught me a lot about sensors and what you can build for really, really cheap.

Researchers from Morocco, the UAE, Egypt, Italy, and South Africa have developed a low-cost IoT- and fuzzy logic–based irrigation system that dynamically adjusts watering using real-time soil and ...

Capacitive sensors, on the other hand, can be isolated from the water itself, and thus sense the levels without being subject to such degradation.