Many statistical textbooks lend themselves readily to the analysis of physical and chemical data. This is due to the material gathered from such analyses, following, in most cases, normal distribution. Normally distributed data can be examined over time to allow the obtained profile to be studied for variation. Microbiological data rarely follows such distribution. However, such approaches can be adapted for non-normally distributed (or skewed) microbiological data. This paper applies Shewhart Control Charts to the trend analysis of microbiological data from two different pharmaceutical water systems.