Quality Control of Water Production Process Using Multivariate Control Charts

Abstract

Water is very important for life, no life in the world can exist without the availability of water. Turbidity, organic substance, and chlorine residual are the main characteristics of water quality. To monitor the quality of a water production process, Multivariate Exponentially Weighted Moving Covariance Matrix (MEWMC) control chart is used for monitoring the stability of the covariance matrix of a process, and Multivariate Exponentially Weighted Moving Average (MEWMA) control chart is used for monitoring the stability of the mean vector of a process. In this study, the optimum λ for the MEWMC and MEWMA control chart for the water production process during the dry season and the rainy season is λ = 0.1. The variability of water production process during both dry and rainy seasons is in control, while the mean of water production process during both dry and rainy seasons is not in control. Based on the analysis of process capability, it is known that the water production process during the dry season and rainy season is capable of producing water with turbidity level that meets the specification limit, but is not capable to produce water with organic substance and chlorine residual that matches the specification limit.