This chapter aims to provide information on the progress of research into water quality analyses, providing an overview of the state of the art, including novel research achievements, in the detection of water contaminants. After a brief introduction to the main sensing systems’ characteristics, the attention will be devoted to two different classes of pollutants: organic and inorganic. Microbiological analyses concerning the monitoring of bacterial load in water and chemical analyses with a special focus on mercury, related to heavy metal pollution, and nitrogen compounds, i.e. nitrate ion and ammonium ion, are discussed. Particular attention will be devoted to all sensing systems that are in principle portable and able to make real-time measurements in situ.