RO is the first process step towards purified water (PW) or water for injection (WFI) that changes the release relevant parameters like conductivity, total organic carbon (TOC) and bioburden. RO can either be applied as single or double pass, depending on the system setup and raw water composition. However, due to the design and functionality of the RO the concentration side of the RO always shows a very high bioburden and mineral concentration. Even if the RO is a very effective barrier, it’s not a 100% delimitation.