Complexometric titration is a commonly used method to test hardness of water. Since small variation of colour is non observable to the naked eye in colorimetric method, it is advisable to use a sensor to monitor the variation of the signal throughout the titration process, which helps to detect the correct end point of the process. This paper discusses the ability of finding end point of titration using colorimetric method. Beer Lambert law was used for computing colour absorbance of the optical sensor. Three colours were transmitted via a solution one at a time, to detect the end point accurately. Less volumes of sample and titrant make an environmental friendly approach. The developed sensor is capable of detecting concentration of hardness from 100 mg/L to 1000 mg/L and automation of the device allows the process with no expert involvement.