Proposal of a Sensor Node to Determine the Suitability of Reclaimed Water for Green Areas Irrigation in Smart City Context

Recently, the potential for reclaimed water for irrigation purposes has been highlighted. Nonetheless, reclaimed water quality can vary over time and the sources; therefore, their control before using it becomes necessary. In this article, we propose a wireless sensor network for monitoring reclaimed water quality in the water grid to evaluate the suitability of water for green areas irrigation. The system comprises sensor nodes and actuator nodes communicated with long range (LoRa) technology. This article focused on the development of the sensors based on two coils and evaluated the effect of the capacitor included in the conditioning circuit on the sensor signal. The novelty of the proposed sensor is that the coils are isolated from the water, and only a portion of enameled copper wire is in direct contact with the water. A total of 14 capacitors were used to select the most appropriate configuration to maximize the signal differences when the water’s salinity changes. Four configurations are analyzed in detail, including a calibration and verification stage. To determine the best configuration, six parameters, including the working frequency, the maximum output voltage, or the average absolute and relative errors, among others, are considered. With an average absolute error of 1.09 mg/L and a working frequency of 812 kHz, configuration 3 has been selected.