This chapter considers attacks on sensors deployed in a water supply system and present a framework to detect such attacks. A cyber physical system (CPS) is a system that tightly combines and coordinates its computational/cyber elements together with physical elements. Wireless sensor communications have been extensively used to enhance the intelligence of CPS, whereas sensors gather information from the physical world and convey it to the central cyber system that further processes the sensor data. The water system is modeled using the Saint-Venant model. The Saint-Venant equations are modeled as hyperbolic nonlinear equations. The Saint-Venant equations are not compatible with the Kalman filter as the filter is designed for linear systems. So, to combine the hyperbolic water system model and the Kalman filter model, the Saint-Venant equations are linearized using Taylor series expansion. The difference between these two values is compared with a threshold to detect if the sensors have been compromised or are at fault.