Statistical Quality Control in Sachet Water Production: A Case Study in Onitsha, Anambra State

The sachet water industry in Onitsha, Anambra State, South East Nigeria, is a critical source of potable water for millions of urban residents, yet product quality remains inconsistent across producers due to inadequate process monitoring. This study applies statistical process control methods, specifically Shewhart control charts and process capability analysis, to evaluate and improve quality consistency in sachet water production at a registered water factory in Onitsha. Daily samples of 10 sachets are collected from three production lines over a 20-week period, with measurements taken for seal integrity, fill volume, turbidity, and coliform bacterial count. X-bar and R control charts are constructed for fill volume and turbidity, with control limits established from the first ten weeks of stable production. Analysis of the subsequent ten weeks identifies six out-of-control signals on the turbidity chart and three on the fill volume chart, indicating assignable causes requiring investigation. Process capability indices for fill volume confirm that the production process is marginally capable with Cpk of 1.04, below the industry benchmark of 1.33. Root cause analysis using Fishbone diagrams links most out-of-control signals to filter membrane degradation and inconsistent operator practice. The study recommends preventive maintenance scheduling and operator retraining as priority corrective actions. Keywords: statistical process control, control charts, sachet water, process capability, Onitsha.