This paper describes the design and evaluation of an Internet of Things (IoT)-driven automated plant watering system that utilizes real-time soil moisture monitoring to control irrigation. The system integrates a soil moisture sensor, an ESP8266 microcontroller, a water pump, and a cloud-based data collection and control platform. Over a period of 6.6 days, the system collected more than 15,000 data samples for comprehensive performance analysis. The results indicated that the IoT-based system achieved high water use efficiency, effectively eliminating missed and unnecessary watering events, while the manual system operating at fixed 12-h intervals achieved only 25% efficiency. An analogy is presented to illustrate how sensor error impacts system performance by introducing an error of ±5% in soil moisture readings. Under these conditions, the system maintained high performance, with only a slight reduction in water efficiency to 96.88% and a minimal increase in leakage and overwatering incidents. While the system performs well in a controlled, small-scale setup, the study emphasizes the importance of real-time data validation to ensure reliability when scaling to larger applications. This work demonstrates the potential of IoT-based irrigation systems to enhance water management and provides practical insights for the future development of smart agriculture solutions.