A plant watering robot fails when it trusts one cheap soil sensor forever. Soil probes corrode, pots drain differently and pumps siphon if tubing is routed badly. A robust build combines moisture thresholds, dose limits and leak detection.
Use a peristaltic pump or diaphragm pump so water only moves when commanded. Add a reservoir level sensor so the pump does not run dry. For indoor plants, a leak sensor under the pot tray is more important than fancy AI.