Quality of Water Production Process Using Mixed Multivariate EWMA-CUSUM (MEC) Control Chart

Human life is highly dependent on clean and freshwater. Therefore, the quality of water used by humans must be properly monitored and controlled. Based on the regulations of the Ministry of Health, the quality of clean water can be monitored from the parameters of physics, chemistry, and microbiology. The main characteristics of water quality are turbidity level, organic substance, and chlorine residual which are correlated with each other. This research proposes the combination of MEWMA and MCUSUM charts called MEC control chart for monitoring the process mean of water quality with the variables used are turbidity level, organic substance, and chlorine residual. This charting method is divided into two-part, namely MEC1 and MEC2. Further, the water production process is characterized by dry and rainy seasons. Based on the analysis results, it is found that the optimum λ in the production process during the dry and rainy season for the MEC1 control chart is 0.3. Meanwhile, the optimum λ in the production process during the dry and rainy season for the MEC2 control chart is 0.1. In this condition, the MEC1 control chart is more sensitive than the MEC2 control chart because of the higher number of out of control observations. Moreover, the organic substance is the main issue causing the out of control observations during the dry and rainy season. In the capability process analysis, the process of water production during the dry and rainy season is said to be capable because the capability index of the turbidity level is larger than the specification limit. On the other hand, the water production process with organic substance and chlorine residual are not capable due to the lower capability index compared to the specification limit.