To be certain, you'll need to:
1. Consult your vehicle's repair manual: This is the most reliable source. The manual will have diagrams showing the exact location of all sensors.
2. Look for a sensor with a single wire: The water temperature sending unit usually only has one wire connected to it. It's a relatively small sensor.
3. Check near the thermostat housing: This is the most common location. The thermostat housing is located at the top of the engine, near the front.
4. Look for a sensor in the area where coolant hoses connect to the engine: Coolant flows in this area which is where this sensor is most often located.
Be cautious when working around hot engine components. Allow the engine to cool completely before attempting to locate the sensor.