Q: Do reverse osmosis filters remove bacteria? How?
A: Yes, bacteria will be removed via reverse osmosis due to size exclusion (i.e. the bacteria are larger than the pores in the reverse osmosis membrane so they can’t pass through). However there can be defects in the membranes which allow the bacteria to pass through. I’ve also seen it hypothesized that the bacteria will move around the o-ring which typically seals the reverse osmosis into place within its housing. Secondary contamination, where bacteria will move up the pure water stream and attach to the membrane, is also a possibility. This is why while bacteria can be removed via reverse osmosis, these systems are rarely certified to be microbiological purifiers.