ESPiezometer: ESP32-based field tool for installation and validation of piezometric sensors for groundwater level monitoring.

Field installation of piezometric sensors often involves uncertainty regarding correct placement, sensor response, and agreement with manually measured static water levels. Commercial dataloggers provide high-resolution monitoring but do not offer installation-stage validation or open access to communication protocols. To address this gap, the ESPiezometer was developed as a low-cost, open-source device based on an ESP32-C3 microcontroller with RS485 Modbus communication, on-board water level calculation, temperature-based density correction, and Bluetooth Low Energy (BLE) integration for field data logging via an Android application. The hardware enables real-time verification of raw and corrected water level readings during deployment and allows immediate comparison with manual measurements. A custom PCB and 3D-printed enclosure were designed to facilitate reproducible assembly and portability. Field validation in a groundwater observation well (30-90 m depth range) demonstrated consistent communication integrity via CRC checks and measurement repeatability with a standard deviation below 0.03 m. After density correction, measurement error was reduced by 35-50% relative to manual reference levels. The obtained results demonstrate that the ESPiezometer can serve as a reliable companion instrument, reducing uncertainty during deployment and improving confidence in long-term groundwater monitoring campaigns.