An environmental measurement system was developed using a low-power sensing module, IEEE 802.11 (Wi-Fi) connection module, and a small solar cell and battery. An Arduino-based sensing module was used for many kinds of analog/digital outputs sensors with the Arduino software library. The data from the module were sent via Wi-Fi HTTP(S) clients operation, and collected by MySQL server using PHP (Hypertext Preprocessor) uploading code. The sleep and wakeup strategy controlled by a real-time clock achieved an average system power consumption of 18 mW. The system also checked its own condition by measuring battery voltage and temperature. It operated on a small 0.8 W solar cell and 1500-mAh Lithium iron phosphate battery. Data on the MySQL server were downloaded, and visualized the sensing data on Google Maps. Visualizations and log data help users understand environmental contamination levels in a farm, garden, forest, etc.