The Internet of Things (IoT) represents the enabling paradigm of a huge number of smart applications, spanning from short-range communications to Low-Power Wide-Area Network (LPWAN). Among them, environmental monitoring becomes more and more challenging as the area of interest is difficult to reach. The present contribution proposes WaterS, an open-source project that relies on low-cost and rapid-prototyping technologies. It tackles the main challenges of remote water quality monitoring systems taking advantage of the Sigfox protocol stack. The realized experimental setup is able to gather geo-referenced water quality measurements. Finally, it successfully addresses self-sufficiency thanks to solar energy harvesting.