Reverse osmosis (RO) process is widely used for water desalination and reclamation. However, the process is challenged by membrane fouling; the formation of a deposit layer on the RO membrane surface due to the accumulation of rejected particles/bio-materials/organic matters/solutes. Membrane fouling is inevitable, thus effective control and cleaning strategies are critical for the sustainability of the process. To implement the control or cleaning process, it is important to monitor the state of the process which typically involves measurement of pressures and flows. These are crude measurements and fail to detect incipient fouling. Here, we present fouling monitors that are based on a side-stream RO cell simulating the flows in the plant, where the incipient foulants will be detected by non-invasive methods of Electrical Impedance Spectroscopy (EIS) and Ultrasonic Time Domain Reflectometry (UTDR). The EIS involves measuring the electrical properties across the device via small electrodes either side of the membrane while the UTDR applies an acoustic signal that reflects from interfaces i.e. membrane, fouling layer etc.