In order to estimate the data integrity risk of microbiol. tests and then adjusting the level of mitigation actions based on the risk intensity, risk matrix tools may be used. In microbiol. testing, excursions occur when measurements differ from the acceptance criteria or normal/expected values. In cGMP environments, an excursion requires a thorough investigation, a root cause assessment and actions to resolve the excursion, and prevent reoccurrence in the future. The following types of excursions may occur in microbiol. testing: out of specification, exceeding the action level, exceeding the alert or out of expectation level, and out of trend. Many excursions in water microbiol. monitoring come from contamination during sampling. These excursions are the most complex to investigate as many factors may impact the final microbiol. quality of non-sterile drug products. For excursion with environmental monitoring it is advisable to distinguish between critical and noncritical excursions.