Water quality is crucial for public health, especially in areas with water scarcity, such as remote islands. Although reliable measuring devices are available, on-site manual testing, such as in water tanks, is still necessary. In order to determine the quality of drinking water, a set of measurements should be carried out automatically, at regular intervals and without delay, thus ensuring the monitoring of its suitability. In this research work, an integrated low-cost water quality monitoring system is presented. The proposed system consists of the monitoring stations and an information system. Each monitoring station includes a microcontroller and sensors, and is installed in the water reservoir, while the information system is used to capture, store, and visualize the measurement data. Data transmission is carried out over a long-range (LoRa) network, providing extensive coverage for receiving data from Internet of Things (IoT) devices. Additionally, linear and non-linear correction factors are proposed to improve the accuracy of measurements from low-cost sensors, resulting in more reliable data. In this way, the end users, such as local authorities or citizens, are given the possibility of immediate information on water quality via the web.