Turbidity is one of the key water quality parameters in environmental monitoring, water treatment or industrial process operation. Turbidity is however very challenging to measure reliably due to the many factors affecting the reading and functionality of the measurement device. In this paper, the results of the experiments to study the effects of changes in water quality and environmental condition to the readings of turbidity measurement devices are presented. The experiments were carried out in stable laboratory conditions where controlled changes were made to water pH, the temperature, salinity, colour, environment brightness and the mixing speed of the water. The study showed that even though the actual turbidity of the water remained constant the changes in other variables caused in the worst-case significant disturbances to the turbidity measurements. This knowledge is vital, for instance in monitoring or developing a robust model for forecasting regional turbidity in natural waters.
Keywords: Measurement uncertainty; on-line sensor; turbidity; water colour; water quality.