Water plays an essential role in our lives, but the vast increase in global industrialization, rural to urban drift, population growth, modernization, high use of fertilizers and other chemicals in farms, mining, and construction practices have deteriorated the available water quality to humans. In fact, the unsustainable use of water resources has contributed immensely to its reduction in many parts of the world. The quantity of freshwater present on earth is only about 2.5% which makes it one of the most valuable resources needed for human survival; hence, it must be carefully monitored and maintained globally. Poor water and sanitation conditions can lead to waterborne diseases in humans like cholera, typhoid, diarrhea, and dysentery and are estimated to cause millions of cases annually. This makes up monitoring of water a concerning issue because a water monitoring process involves tracking of changes taking place in water quality over time, identifying emerging as well as existing problems, and designing appropriate and effectual intervention programs to reduce water pollution and maintain aquatic health. Monitoring water quality is also important in supplying safe and clean water to human population, preventing the outbreak of diseases related to water. Thus, a reliable assessment of water quality at regular interval is necessary for its safe usage. The water quality is usually tested in terms of its physicochemical and biological parameters such as color, temperature, turbidity, electrical conductivity, pH, hardness, DO, BOD, COD, microorganisms, etc. which demonstrates the overall health of an aquatic system. Heavy metals such as mercury, lead, cadmium, chromium, etc. are also of major concern due to their toxic nature in water. Therefore, in this chapter, we review various techniques/methods to monitor the quality of water.