While there are some differences between the various pharmacopoeias on the exact specification for some impurities, the general consensus is that the following impurities should monitored:• Conductivity• TOC• Endotoxin (for WFI only)Some pharmacopoeias also require testing for heavy metals and nitrates. Consult applicable monographs for exact specification.While bacteria testing is not a monograph requirement, all pharmaceutical companies sample and test for bacteria. The pharmaceutical industry references the 1993 US FDA “Guide to the Inspection of High Purity Water Systems” [1] which stipulates the following maximum bacteria action limits for pharmaceutical water systems:• Bacteria action limits at or below 100 cfu per ml for PW• Bacteria action limits at or below 10 cfu per 100 ml for WFI